ccache: Fix for distcc cross-compiling / various improvements (#1026)

* ccache: Fix for distcc cross-compiling / various improvements

* Make ccache work when cross-compiling with distcc (fix #716)
* Allow to configure the ccache size in "pmbootstrap init"
* Moved ccache stats code from pmb/build/other.py to
  pmb/helpers/frontend.py
* Grouped job count, ccache size and timestamp based rebuilds
  together to "build options" and allow to skip them
* Sorted config options that had to be modified anyway
  alphabetically

* Improve comment in arch-bin-masquerade APKBUILD