speed up page generation by making avatar lookup occur at the browser
not at page generation

* Protect against evil email address ".."

* hash the complete email address

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Cache last commit to accelerate the repository directory page visit

* Default use default cache configuration

* add tests for last commit cache

* Simplify last commit cache

* Revert Enabled back

* Change the last commit cache default ttl to 8760h

* Fix test

Co-authored-by: Lauris BH <lauris@nix.lv>

Signed-off-by: Tamal Saha <tamal@appscode.com>

* Add commit count caching

* Small refactoring

* Add different key prefix for refs and commits

* Add configuratuion option to allow to change caching time or disable it