Load lcov format files to show code coverage

[virtuald]

After I use gcov/lcov to create a coverage file, it would be really useful to be able to load that into sourcetrail and see coverage data while browsing the code.

It seems to me that it would make the most sense to not load the lcov files into the database, but only have them temporarily in memory? Though, I guess if it were separate tables, then it would be pretty easy to just clear them without disturbing the other data.

I expect the easiest thing to implement would be coloring the lines of source files, similar to how lcov's genhtml does it now. It would be really cool to color the graph nodes according to their coverage too, but that's probably harder?

In the general case, it would be useful to be able to have user-specified annotations/colors at each node of the graph and for each line of code. It's not clear to me whether a coloring thing for showing coverage should be built off that or if it should be a separate thing.