Consolidate Issue filter actions to one controller action

[pulponair]

Currently we have:

• All isses
• Filtered by language
• Filtered by label.

I would suggest to consolidate that to a single issue and make the filter potentiallly combinabile. so urls would look like:

/i/?filter[language]=php&filter[label]=feature etc. That would drastically reduce the amount of code in controller and view.