fabfile: create the 'pootle/assets' folder

before building the static data
make MIN_SIMILARITY for fuzzy matching configurable
precommit hooks return an array of files
preupdate hook returns a new file

only accepts one path not an array of paths

refs #2682
run the postupdate hooks before updating the stores

this allows the hook to modify the new data
call precommit and postcommit hooks when adding files
add "pretemplateupdate" hook

This hook is called before updating a file from the template.
The hook can prevent the updating with a False return value.
add hook template for add-ons
enable Android Resources as translation file type