Display decklist content

This MR is marked as Draft as it depends on !184 (merged), which should be reviewed first, as it prepares the important part of the code.

So this MR adds the code for basic interaction with the decklists (viewing, editing).

Things still missing, that will be addressed later:

• Autocomplete for the card names
• More validation (including banlists)
• Creation of new decklists in a Collection