Issue title: Templates not installed on Linux 
 Issue body: I installed the monogame-sdk for linux, version (203)339-6732.  No templates were installed.
I can run my existing projects, but I'm getting frustrated trying to creating a new game without a template. 

elementary OS 0.4 Loki (64-bit) Built on "Ubuntu 16.04 LTS"
monodevelop version 6.1.1

Interestingly, the install couldn't tell that I have version 6 of monodevelop installed:

Verifying archive integrity... All good.
Uncompressing Monogame Pipeline Installer...........................................................................................
Dependencies:
 - mono-runtime...................................[Found]
 - gtk-sharp3.....................................[Found]

Optional Dependencies:
 - MonoDevelop 6..................................[Not Found]
 - Rider..........................................[Not Found]
 - referenceassemblies-pcl / mono-pcl.............[Found]
 - ttf-mscorefonts-installer / mscore-fonts.......[Not Found]

Continue (Y, n): Y
Installing MonoGame SDK...
Creating launcher items...
gtk-update-icon-cache: Cache file created successfully.
Adding mimetype...
To uninstall MonoGame SDK you can run "monogame-uninstall" from terminal.

 Comments: 
 Comment 0: Ok, so I actually installed version 6 because of the message in the monogame-sdk install log. It didn't help that. But I've noticed that it does return the monogame addin to the addins menu. So I was able to install it there. So this is solved, I guess.

The last time I upgraded, I had to switch from the addin to the nuget. Now we switch from nuget to install script. Now back to addin. 
I waste a dis-proportionate amount of my time trying to cope with breaking changes on ever minor version change. It would be nice if there were some documentation or road map or something so that people who are not insiders can tell what's going on. 

{'source': 'GithubIssues', 'repo_name_with_owner': 'MonoGame/MonoGame', 'issue_id': 187625841, 'repo_stars': 8884.0}