Fixed switching between items and recipes clearing the level filter

When a user sets a filter on an item-search and then switches over to the recipe-search he will keep the min / max level filters he applied.

TODO: 
- [x] The level filter on the recipe search should actually filter the level of the resulting item and a **rating** filter could be introduced to filter the rating (done).

@rubensayshi: I hope you are fine with me opening a bazillion pull requests. If I should group my edits in broader categories I could do that too. (It just helps me to keep related changes together in separate pull requests).