Make optional rule to update desktop cache database

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=705249
Fixes SF bug #92
build: Enable AM_SILENT_RULES
tests: Fixes filenames
build: simplify Makefile rules for pybrc
build: fix make distcheck

* Remove helper scripts install-check
* Use intltool macros instead of manual handling for translation files
* Add missing definitions to clean up
* Add missing files to translate
build: Add path to PYTHONPATH

It only worked if the path por Pyblio was already in the PYTHONPATH