Replace constructors with Builder only.

[stefanuebe]

There are still some legacy constructors, that need extra mainenance, but can be easily replaced with the builder. Therefore we should deprecate and remove those constructors (except for the no args one).

To make migration easier, we can provide static methods to the FullCalendarBuilder, e.g. createInstance(JsonObject initialOptions) and createInstance(int maxEntriesPerDay). This part is optional as the FCB itself is relatively simple to use.