Initial commit of kdiff3

Summary: Inclusion of kdiff3 into Solus repository. Fixes T5897.

Test Plan: Created a simple git repository with two conflicting branches. Merged branch2 into master by solving the conflict with kdiff3.

Reviewers: Triage Team, JoshStrobl

Reviewed By: Triage Team, JoshStrobl

Subscribers: JoshStrobl, Girtablulu

Maniphest Tasks: T5897

Differential Revision: https://dev.getsol.us/D9222