Global search of issues over all repositories in web interface

[scullhead]

• Gitea version (or commit ref): 1.4.0+3-g641d481
• Git version: 2.7.4
• Operating system: Ubuntu 16.04.4 LTS
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant

Description

When you are on the "issues" tab of a repository you have a search input field where it is possible to search for a text in all issues of this repo.

When you klick on "Issues" in the global navigation menu of gitea it shows a list of all issues from all repositories (if they are public).
It would be very useful if there was also a search input field to search over all public issues.

[stevegt]

Possible dup of #2434 -- discusses backend.

[lunny]

Please discuss on #2434. @scullhead could you paste your issue content on #2434 as a comment I think it's very useful.