Add an option to filter the "kind" of the release

[ArnaudLigny]

3 cases:

1. release
2. pre-release
3. "just" a tag

Example:

[j0k3r]

Few questions:

• will you be able to select more than one option?
• what will affect that choice: dashboard and/or rss feed?

Some repos doesn't use tag at al, some other doesn't use release at all and some of them use a both. At the moment, I don't make difference between a tag and a release (but I do about pre-release).