* DB schema improvements
- add column DragonId to table PairData
- add foreign keys for table PairData
- remove unused column InventoryId from Vikings table
- simplifying relations viking -> selected dragon
- remove SelectedViking and SelectedVikingId from Dragon
- remove column SelectedVikingId from Dragons table
- cleanup and arrangement code in DBContext.cs
* support for dragons PairData in KeyValueService
and in "pairs" API endpoints
* GetPetAchievementsByUserID and enum for PointTypes
* add RankService
* use AchievementPointTypes for PointTypeID
... insted of int in schema
* support for player XP, fix dragon XP
- database table
- return correct value in API call
- save XP from mission
* rename RankService to AchievementService
* use addAchievementPoints for all non item reward
this could be a good place for wallet servicing too ... so currency reward too
* return const XP value for farming and fishing
we don't have gathering method for those XPs yet
* fix avatar schema, fix coding style
