[Feature] Issue 245 - Variable Image Width BY wells

IMPORTANT: This is a commit developed originally by the user “wells” in
GitHub: https://github.com/wells

https://github.com/wells/FlexSlider/commit/c81800662dd25b594a3648bd52be9
4ac4cd9585a#diff-81eb7c82b8c37aca5f60ec7ddc1f95a3

I needed urgently a rebase of the current FlexSlider version with this
old commit so as a quick solution I’ve done it manually in a local
branch.
Merge branch 'Issue245'