CFile: add constructor for std::string, facilitates the use of string's.
bouquets/alternatives: add search path for bouquet's and alternatives' files.

Search path:
 - [enigma2_config]/.
 - [enigma2_config]/bouquets
 - [enigma2_config]/alternatives
In this order.

Rationale:
 - less clutter in the enigma2 config directory (especially if
   you have lots of alternatives)
 - possibility to link or mount one of the subdirectories to a
   shared disk e.g. on a NAS, so you can keep one set of
   bouquets/alternatives for all receivers.

Drawback: new bouquets and alternatives will always be created in
the default location, so you'll have to move them manually, if you
want them in one of the non-default directories.
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2