Properly handle statfs on FreeBSD

* FreeBSD doesn't need statfs64 as regular statfs uses 64 bit types
* FreeBSD uses different headers for statfs
Add desktop file
Add installation support to cmake
Fix variable name
Merge pull request #62 from AMDmi3/statfs

Properly handle statfs on FreeBSD
Merge pull request #63 from AMDmi3/install

Add installation support to cmake
Merge pull request #64 from helgp/master

Followup on invalid panel path err. All test cases work now.