ddddce0 util: Replace boost::signals2 with std::function (MarcoFalke)

Pull request description:

  This removes the `#include <boost/signals2/signal.hpp>` from `util.h` (hopefully speeding up the build time and reducing the memory usage further after  #13634)

  The whole translation interface is replaced by a function `G_TRANSLATION_FUN` that is set to nullptr in units that don't need translation. (Thus only set in the gui)

Tree-SHA512: 087c717358bbed8bdb409463e225239d667f1ced381abb10e7cd31a41dcdd2cebe20b43c2ee86f0f8e55d53301f75e963f07421a99a7ff4c0cad2c6a375c5ab1

fa5ce27 ui: Compile boost:signals2 only once (MarcoFalke)

Pull request description:

  ui is one of the modules that poison other modules with `boost/signals2` headers. This moves the include to the cpp file and uses a forward declaration in the header.

  Locally this speeds up the incremental build (building everything that uses the ui module) with gcc by ~5% for me. Gcc uses ~5% less memory.

  Would be nice if someone could verify the numbers roughly.

  I presume the improvements will be more pronounced if the other models would stop exposing the boost header as well.

Tree-SHA512: 078360eba330ddbca4268bd8552927eae242a239e18dfded25ec20be72650a68cd83af7ac160690249b943d33ae35d15df1313f1f60a0c28b9526853aa7d1e40

# Conflicts:
#	src/interfaces/node.cpp
#	src/noui.cpp
#	src/ui_interface.h

ddddce0 util: Replace boost::signals2 with std::function (MarcoFalke)

Pull request description:

  This removes the `#include <boost/signals2/signal.hpp>` from `util.h` (hopefully speeding up the build time and reducing the memory usage further after  bitcoin#13634)

  The whole translation interface is replaced by a function `G_TRANSLATION_FUN` that is set to nullptr in units that don't need translation. (Thus only set in the gui)

Tree-SHA512: 087c717358bbed8bdb409463e225239d667f1ced381abb10e7cd31a41dcdd2cebe20b43c2ee86f0f8e55d53301f75e963f07421a99a7ff4c0cad2c6a375c5ab1

# Conflicts:
#	src/bench/bench_dash.cpp
#	src/qt/dash.cpp
#	src/qt/splashscreen.cpp
#	src/qt/transactiontablemodel.cpp
#	src/test/test_dash.cpp
#	src/util/system.h
#	src/wallet/coinselection.cpp

fa5ce27 ui: Compile boost:signals2 only once (MarcoFalke)

Pull request description:

  ui is one of the modules that poison other modules with `boost/signals2` headers. This moves the include to the cpp file and uses a forward declaration in the header.

  Locally this speeds up the incremental build (building everything that uses the ui module) with gcc by ~5% for me. Gcc uses ~5% less memory.

  Would be nice if someone could verify the numbers roughly.

  I presume the improvements will be more pronounced if the other models would stop exposing the boost header as well.

Tree-SHA512: 078360eba330ddbca4268bd8552927eae242a239e18dfded25ec20be72650a68cd83af7ac160690249b943d33ae35d15df1313f1f60a0c28b9526853aa7d1e40

# Conflicts:
#	src/interfaces/node.cpp
#	src/noui.cpp
#	src/ui_interface.h

ddddce0 util: Replace boost::signals2 with std::function (MarcoFalke)

Pull request description:

  This removes the `#include <boost/signals2/signal.hpp>` from `util.h` (hopefully speeding up the build time and reducing the memory usage further after  bitcoin#13634)

  The whole translation interface is replaced by a function `G_TRANSLATION_FUN` that is set to nullptr in units that don't need translation. (Thus only set in the gui)

Tree-SHA512: 087c717358bbed8bdb409463e225239d667f1ced381abb10e7cd31a41dcdd2cebe20b43c2ee86f0f8e55d53301f75e963f07421a99a7ff4c0cad2c6a375c5ab1

# Conflicts:
#	src/bench/bench_dash.cpp
#	src/qt/dash.cpp
#	src/qt/splashscreen.cpp
#	src/qt/transactiontablemodel.cpp
#	src/test/test_dash.cpp
#	src/util/system.h
#	src/wallet/coinselection.cpp