middleware: move handling of permanent repo URLs to separate middleware This is about the handling of repo URLs like '_123' for the repo with repo_id 123. The de-mangling of such URLs was spread out across multiple layers. It fits much more nicely as a middleware layer. The code in routing and simplehg / simplegit can thus be removed. The base _get_by_id function was confusing - fix it by removing it. To do that, refactor utils introducing fix_repo_id_name to replace get_repo_by_id. We now assume in the application that we never have any extra leading '/' in URL paths. And while trailing extra '/' might be fine in actual URLs, they must be handled at the routing level, not propagated through all layers. This changeset is not really changing that.

[pytest]
# only look for tests in kallithea/tests
python_files = kallithea/tests/**/test_*.py
addopts =
    # --verbose
    # show extra test summary info as specified by chars (f)ailed, (E)error, (s)skipped, (x)failed, (X)passed, (w)warnings.
    -rfEsxXw
    # Shorter scrollbacks; less stuff to scroll through
    --tb=short