add repair tasks to support fixing known issues
add repair tasks to support fixing known issues

during development, the project might get into a broken state. Many
times, it helps to start all over again, after removing bower_components
and node_modules directories. The `repair` tasks should support those
cases and try to solve all known problems (semi-)automatically.

add silent options to bower and npm install commands, to reduce output.

Open-Xchange-Frontend/shared-grunt-config