Add the ability to group lighthouses

[jeroen1602]

Every users always has at least 2 lighthouses that all have to change power state at the same time. In order to make this task easier.

Add an option to group lighthouses together to change their states all at once.

• Add table to database
  • Create migration for the database
  • Create dao object
  • Create debug page for the new dao
• Create group widget which holds multiple lighthouses
  • Create widget for ungrouped lighthouses.
  • Show known, but offline lighthouses.
• Create mechanism for adding lighthouses to a group
  • Add warning for adding lighthouses with the same frequency
  • Add warning (maybe error) for adding 2 different type of lighthouses
  • Rename/ delete a group.
• Add button for turning on/ off/ asking what to do
  • Do the opposite of the current state if all lighthouses have the same state.
  • Ask the user what to do if not all states are the same or some/ all states are unknown.
• Add info to help page
• Add custom icons for the actions
  • Add icon for change group
  • Add icon for delete group
  • Add icon for rename group

[jeroen1602]

#6 should be implemented first.