Create the "after-update-cmd" config setting

[aik099]

Create the "after-update-cmd" config setting of array type.

1. each line in there is considered as Bash command and will be executed
2. the {wc_path} will be replaced with corresponding working copy path

Maybe the composer.json in the project can be adapted to executed post update stuff and SVN-Buddy will just call it.

[aik099]

Actually Composer's Scripts (see https://getcomposer.org/doc/articles/scripts.md#writing-custom-commands) is the best option currently, because it moves away knowledge of a project in a working copy to the composer.json.

This way calling svn-buddy-update or similar script would do all the needed stuff.