Rework contracts, goals and seasons (Post API)

Now that the API(#69) is in place, I can focus on reworking the visuals of contracts and goals a bit further:

[ ] Completely move season to contracts in back end and treat them like contracts ("type" attribute must be set to "season")
[ ] History should no longer be stored in season scope (All Init entries with 0 XP shall be removed)

History entries should be in a list next to contracts
[ ] Add "bpType" field to differentiate Freepass from Battlepass rewards
[ ] Categorize season contracts with a split toggle button (Active | Passed)

Contracts
[ ] Split ~~agent~~ season and event contracts from eachother with "type" attribute

This is needed because of different categorizations of the contracts, ~~since event contracts are time based and agent contracts are not~~ to show them in separate secions from one another
[x] ~~Pull the color for the progress bars from the API data (Agent contract)~~
[x] ~~If the contract is an agent contract, have the agent icon be shown next to the info~~
[ ] Add "startDate" and store fitting history entries in a list as UUIDs until complete

startDate shall be the date it gets added to the users contracts. For events and seasons this will be as soon as they start, ~~for agent contracts its the moment the user adds the contract~~
[ ] Add "startXP" attribute to offset calculations based on history entries
[ ] Add ability to edit said "startXP" attribute
[ ] Categorize event and season contracts with a split toggle button (Active | Ended)
[x] ~~Categorize agent contracts with a split toggle button (Active | Paused | Completed)~~

[ ] Add icon(s) of the reward item(s) next to the data

If more than one item is rewarded with the same amount of xp (e.g. Free Pass rewards) the icons and names should cycle and there should be arrow buttons on the image, similar to galleries on online shops

BitTim / VexTrack