added camera registers accessors
VBODisplay should be built only if cuda is available
added camera brightness control
shuffled some of the methods around
Revert "added camera registers accessors"

This reverts commit bc5a62445ae19e25b0cb31db8066d11a35fddffd.
Merge (issue #15) branch 'master' of git://github.com/renzodenardi/Pangolin into renzodenardi-master