eitd: Reduce sectionsd memory requirements:

* Various EPG related strings (language- and country keys, audio descriptions) come with a pretty low variance. Cache them, and use an index instead of allocating redundant strings for each and every SIevent.
* Storing content classifications in native format instead of std::string removes quite some memory overhead, too.

This saves about 250 bytes of RAM for every event cached, resulting in a considerably reduced sectionsd memory footprint.

Conflicts:
	src/eitd/xmlutil.cpp
gui/filebrowser: don't crash when fonts are changed (untested)
gui/filebrowser: rework page-up/-down

Conflicts:
	src/gui/filebrowser.cpp
gui/filebrowser: fix page up/down

Conflicts:
	src/gui/filebrowser.cpp
system: mv ping.c ping.cpp
gui/nfs: implement mac address lookup

Conflicts:
	src/gui/moviebrowser.cpp
	src/gui/nfs.cpp
fix gui/nfs

Conflicts:
	src/gui/nfs.cpp
gui/nfs: use configuration value for type

Conflicts:
	src/gui/nfs.cpp
gui/nfs: add default for local dir, autocreate local dir
gui/nfs.cpp: fix merge
gui/fs: fix NFS_TYPE_OPTION_COUNT (and I'm considering to drop lufs completely)
system/set_threadname: fix
driver/pictureviewer/jpeg: remove server-based rescaling code

Conflicts:
	src/system/settings.h
driver/screen_max: don't return negative start coordinates
lib/xmltree/xmlinterface.cpp: use posix_fadvise to try reduce cached pages, while loading huge epg datatmp1
system/helpers.cpp/h:fall back  to cst-next state for 'to_string' handlers

Prevent possible conflicts
configure: move option enable testmenu to enable testing

Testing is also plausible for general usage of other tests or other
experimental code parts.
Apply most impacted parts from branch cst-next into next-cc

Most impacted parts from branch cst-next into next-cc now has been merged.
Splitting of commits are not really possible, because of too large and
insufficient commented source commits. The mostly changes are related to
menu widgets and progressbar sources.

Some clean ups in menu code are unfortunately lost and must be reworked.
CComponentsFooter: add member to add button labels via vector
CComponentsSignals: ad signal OnSelect