Add template pages to GUI
Split template event dialog between parameters and sourcecode
Remove ugly 'Name:' label
Show widgets for the parameters of a templated event
Ensure we can get the values from the parameter widgets later
Add a vertical separator
I have no Internet currently
Can now permanently fill in the parameters of a templated event.
Add Gtk::SourceView to the Gemfile
Highlight the parameter we’re currently editing in the textview
Add an entry for no template to the combobox
Cleanup map grid code
Add an option for highlighting the hovered cell.

As the image grid’s #on_expose signal handler doesn’t currently
take care to only update the requested region, but instead updates
the entire image grid, this option has a heavy impact on the CPU
if activated. Therefore it is off by default.
Add a dialog for generic events
Top widgets for name and ID
Add a dialog for template editing
Display the template pages in the templates dialog
Add widgets for template parameters
Adapt backend’s new conception of template parameters
Implement adding and removing templates