Add Grav to the list of supported CMSs

[urcadox]

https://getgrav.org/

Needs to be tested but it seems like it's only a matter of adding this post-build hook:

cd user/themes/${yourproject} && npm install && ./node_modules/.bin/bower install && ./node_modules/.bin/gulp build:ui

[vvenance]

hello @urcadox has it been tested since ?