camera import: can now get EXIF tags for filenames (#8415)

this is a fairly naive rebase of the previous pull request #350 from @jakeprobst. i haven't tested this, nor have I reviewed the code significantly - i only rebased this on the master branch and tried to keep everything as close as it was intended by the patch author.

i have no idea if the last issue (problems with RAW) was fixed.

it would be nice if someone more familiar with the code and the test suite could take a look at this.

thanks!