hide deleted pages in dashboard and page search - fixes #7844
fix tag encoding issues and tweak html_safety some
adopt page unit tests to new use of flow

We're not using flow: nil anymore.

Also split up the tests for different search paths
ensure Page.to_s returns sth. unique

We use it for caching the access of a given user.

So far it would return sth. like DiscussionPage:0x00000007adc3f0.
The hex number is based on memory allocation i guess. Anyway - they
were getting reused - leading to non deterministic test failures in
 unit/pages/page_search_test.

This might also have been a security issue.
Merge pull request #75 from azul/bugfix/tag-encoding-issues

fix tag encoding issues and tweak html_safety some