Multi camera support

[Molau]

This feature is prepared (tab "stations") but not yet implemented.

The flux viewer should display a list of all cameras which have uploaded data to the database. I want to have a "select all" and "unselect all" button (default: all cameras are selected) and I want to be able to select / unselect every camera individually. On data from selected cameras should be used for the calculation of the plot.

And additionally as prio 2: Once the begin/end time or solar longitude and the year are selected, the cameras which do not contribute data to that interval should be greyed out. That is, I should not be able to select/deselect These, because they do not contribute observations, anyway.