don't use getModelObject anymore
prevent change event emitting before the projectChooser data has been loaded.
otherwise we have multiple change events that trigger reloads upstream
make the monthgraph/monthtable load depend on the projectchooser change event.

we don't load the monthGraph right away, because it will be reloaded anyway
once the projectChooser starts up and fires it's 'change' event.
By just settings the monthState, the projectChoosers change event will
trigger a graph/table reload once it has finished starting up.
This prevents a double initialization of the monthGraph which was sometimes
visible as a visual 'flickering' of the graph
add missing destroy checks in monthgraph and table
remove unnecessary dom emptying from monthgraph.

this change was not intentional, just a line i added by accident and forgot to
remove it.
rename _onProjectChange function to _updateMonthWidget
factor out projectChooser for statistics to enhance readability