Fix IsMouseVisible [WinDX] + [WinGL/Linux]. New IsBorderless [WinDX]

This PR includes the following changes:

- Fix to IsMouseVisible on WinDX platform
- Change to IsMouseVisible on WinGL/Linux platform (can someone test on linux please)
- New feature: IsBorderless, currently only implemented on WinDX. (ill look for other platform implementations later on. http://monogame.codeplex.com/discussions/406437)

I'm still very new to git/github. I made a similar PR over at the now old WinDX repo: https://github.com/SickheadGames/MonoGame/pull/12 but didn't know how to move the PR over to this repo, so I made a new PR and changed some more things.

The reason why I changed IsMouseVisible is because the current implementation seemed a bit hackish and didn't work well.

Someone please test the IsMouseVisible property on linux.

Please give me feedback, thanks :)