Add 'swagger_custom_css_styles' config variable to append custom CSS, combined with multiple recent fixes from pending PR's

[novama-jobs]

Combining solutions revised and tested from other recent pending PRs along with the implementation of the 'swagger_custom_css_styles' optional config variable to append additional custom styles in the html head without the need of alter the default linked css file.

Version updated to 0.9.7b3

[ThermodynamicBeta]

I really need this feature

[billyrrr]

Are there any backward incompatible changes?