Issue #97: Switching to side by side diff should be seamless within the same frame (conservancy/kallithea)

[Sam Jaques]

New issue 97: Switching to side by side diff should be seamless within the same frame
https://bitbucket.org/conservancy/kallithea/issue/97/switching-to-side-by-side-diff-should-be

Sam Jaques:

I love side by side view as many others, but I refused to use this until now.

**Currently**:
- Whole file is parsed and can take a while (yes, we have very big legacy files ;)
- Too many scroll bars (at least 1 horizontally, 2 vertically)
- the complete window is refreshed

**Better**:
Show side by side diff in the same frame, and only load the differences like it is done in the standard view. Extending to the complete file should be an option.