Expand functionality of code changes in diff page (Files block)

[webdevelopland]

1. For every change, you take 5 lines before and 5 lines after - that's 1 block. Between blocks you have some separation.
2. Separation can be manipulated, e.g show 5 more lines, or show whole file.
   As you try to find the first block, you might find that when you add 5 more lines, you find another change, and 5 lines after it ends, another change, and then you end up with 1 big block. That's fine.

In a single file, all blocks are expanded together.
The reason for the blocks, is that imagine a file with 1000 lines, and line 15 and line 80 were changed. We don't want to see the whole file.
We'll see only lines 10-20, 75-85 (up to off-by-1)

In every place where lines are hided, here will be a separation.

[webdevelopland]

PR: #488