Move some manager classes to SharedGameResources

The below objects are moved to SharedGameResources. Local references to these objects are removed from various classes. This simplifies access to these objects and removes a small amount of code. Probably an unnecessary change, but when such objects needs to be accessed from a class which is several steps away from GameStatePlay, its a little awkward.

PowerManager
MapRenderer
EnemyManager
CampaignManager
ItemManager
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