Improve performance of showing diffs in the browser

• Gitea version (or commit ref): release/v1.1
• Git version: 2.11.0
• Operating system: GNU/Debian 9
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
  • Not relevant
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist: /
• Browser: Firefox 52.0 (64-Bit)

Description

If you want to display some diffs while comparing, your browser may slow down. One should think about use somekind of async ajax loading.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.