Set Calibre as the default MOBI generator

[Delivers #73631878]
Issue pull request for branch 73631878-calibre-default

[Delivers #73631878](https://www.pivotaltracker.com/story/show/73631878)
[Delivers #73510084](https://www.pivotaltracker.com/story/show/73510084)
[Delivers #73268246](https://www.pivotaltracker.com/story/show/73268246)
[Delivers #72145828](https://www.pivotaltracker.com/story/show/72145828)
[Delivers #70812746](https://www.pivotaltracker.com/story/show/70812746)
[Delivers #69782146](https://www.pivotaltracker.com/story/show/69782146)
[Delivers #60244750](https://www.pivotaltracker.com/story/show/60244750)
[Delivers #70183740](https://www.pivotaltracker.com/story/show/70183740)
[Delivers #69120810](https://www.pivotaltracker.com/story/show/69120810)
[Delivers #68747820](https://www.pivotaltracker.com/story/show/68747820)
Utils#path default argument
rspec version
Add svgnames colors
Add svgnames colors
Merge branch '73631878-calibre-default' of https://github.com/softcover/softcover into 73631878-calibre-default
Remove private beta from template

[#73631878]
Merge branch '73631878-calibre-default' of https://github.com/softcover/softcover into 73631878-calibre-default
Bump version number
Merge pull request #108 from softcover/73631878-calibre-default

73631878 calibre default