Merge / and /gitmanager pages

[lainets]

The two pages are very similar, and the / page doesn't really have much on it. The / page is very slow to load and causes a lot of errors due to it trying to load all configs for all courses found in the database. Loading the configs is only required for the name of the course, which isn't really needed, so there is no need to load the configs.

Thus, all that is needed to merge the two pages is to add the links to the course contents on the /gitmanager page, and the page should be moved to /. Some fiddling is needed with the URLs to make them make sense after this change.

There is also the possibility of removing the / and course content pages and collapsing the /gitmanager URLs to / (e.g. /gitmanager/updates becomes /updates). This would be a good option if it is decided that the course content pages aren't needed.

[markkuriekkinen]

I suppose one easy way to manage the URL changes is to keep them as they were, but add a http redirect from / to /gitmanager. Everything else already works fine.