Fixes timestamp

Fix #1846, #1849  and a bug when we remove/add  a timweEnabled layers the time selector status was not updated.

Test [here](http://mf-geoadmin3.dev.bgdi.ch/dev_timestamp2/?X=164944.36&Y=621295.11&zoom=5&lang=de&topic=dev&bgLayer=ch.swisstopo.pixelkarte-grau&catalogNodes=9900&layers_timestamp=19881231,19041231&layers=ch.swisstopo.zeitreihen,ch.swisstopo.zeitreihen)
Just curiouse: why is this needed?