Implement search by label severity for posted issues under bug reporting phase

[SAN-MUYUN]

Summary:

Implement filter by severity feature for reported bugs under bug reporting phase.

Changes Made:

Besides the original search input box, a new dropdown box is implemented to filter the issues by their severity. Initially, all issues are displayed without any filtering by default.

In dropdown, users can filter the issues by choosing various severities. The severities are taken from label service.

By choosing a severity, only issues with corresponding severity will be displayed. The other issues are hidden.

When used together with original search function, the issues will first be filtered by Search parameter, followed by the severity.

Choosing the None tab will display all issues filtered by Search parameter only.

Proposed Commit Message:

Implement filter by severity feature for issues created under bug reporting phase.

When used together with search, the issues will be filtered by the search parameter first, the remaining issues are then filtered again according to severity.

The severities in dropdown are obtained through label service.

This feature might be very useful for dev team response phase, when large number of reponse is received by the dev team.