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
Updated Spanish translation
Improve punctuation in translatable strings
Updated Polish translation

Actually, it's just "fuzzy" tags removal.
Updated Czech translation
Updated Brazilian Portuguese translation
Updated Greek translation
Updated Hungarian translation
Updated Serbian translation