Issuable sorting should be stored per page
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### Description
For now issuable sorting is stored in cookies as a global value per domain.

That means, if you set some sorting on a page A, it also will be set on a page B.
Steps to reproduce:
1. Open Issues List page. Set sorting to, say, `Priority`. Wait until page is reloaded.
2. Open Merge Requests page. The sorting is already set to `Priority`. Change it to anything else, then go back to the issues list page and you'll see the sorting is changed again.
### Proposal
Store sorting values per issuable.
issue