app: receive the user instead of team slice in the CreateApp function
api: fix code that use app.CreateApp

Now the function requires a user object, not a slice of teams.
app: fix code formatting
app: starting to implement reserveUserApp action

Forward is ready, let's work on Backward :-)

Related to #382.
app: return map in the reserveUserApp action

This will make backward easier.

Related to #382.
app: implement reserveUserApp.Backward

Related to #382.
app: improve docs for reserveUserApp
app: added reserveUserApp.MinParams

This action requires three parameters (app, units and user).
app: provide the user to the pipeline executor in CreateApp

Related to #382.
app: reserve app in the user quota when creating the app

RemoveApp is not releasing it yet. Please hold on :)

Related to #382.