Figure out what to do with premailer dependency

[mbohal]

Currently the project depends on the grunt-premailer npm package which depends on ruby and the premailer gem.

Currently ruby is not installed in the docker container and the grunt mail command therefore fails. There are two options how to resolve this:

1. Get rid of the grunt-premailer dependency and build mail templates by some other means
2. Install ruby and the required premailer gem into the docker containers

I think solution 1. is preferable as it would simplify the stack and make development and contributions easier.

[mbohal]

After discussion with @adamkudrna the premailer/ink stack for generating email template has been removed. It is not maintained anymore and it was not possible to keep it around after removing bower.

It has no effect on current installation. The only problem will be when changes will have to be made to the existing email template. When that happens another solution will have to be found.