feature: Filter by label

[JannikStreek]

Further Notes

As a user I want to filter by label. This should be configurable only by the administrator and should be applied for all users inside the brainstorming. It can be allowed in admin settings for all users.

Checklist

• When a label is clicked, a filter for that label should be applied
• Filter is applied for all users and synced with server. All users should look at the same data. Its a brainstorming and the real world case would be a board where people look always at the same post its. If the board is "filtered" the view is the same for all users.
• The filter is applied on all lanes. This is an addition to the sorting feature which only works per column.
• If a filter is applied and a manual sorting is done and more cards are added e.g. by removing the filter. The current sorting should still be there. It takes precedence over what was there before. The first filter overwrites the sorting which was before given. Example: Red 1, Red 2, Red 3, Green 4, Green 5. Sorting by green and change of positions. Green 2, Green 1. Now Red is added back in. Green 2, Green 1, Reds in some order.
• Adding a filter: The first filter resets all positional ordering. Any additional filter applied appends the new cards directly behind the first filter positions. If the filter is removed at all, its the same logic.
• Removing a filter: Elements are added to the end, sorting is based on the available data and positions recalculated.