Add initial LineCompare component with line numbers.

[rars]

I'd like to add to this library something that is similar to a line diff you might find in a diffing tool for code reviews. This is related to issue #3 and #2.

This PR is an initial concept. It adds CSS classes so that it is easier for clients to customise the appearance of the diff. I'd like to improve it further by adding an option for only showing the context around actual diffs, e.g. showing +/- 5 lines above and below an Insert/Delete but hiding the rest of the Equal portions. This makes it easier to review diffs of large files that only have a few changes.

I thought I'd raise this PR to see if anyone had any thoughts on this before spending too much time on it.

It can be used like the following:

<dmp-line-compare [left]="left" [right]="right"></dmp-line-compare>

Here is an example of the result in Chrome:

[btang28]

Hi,

I tried testing this with an xml compare, instead of having them compare line by line, it sort of compared the entire file.