Backlog search & filter

[Feuermagier]

Fixes #67

I've also moved the backlog code into its own class since it became quite large.

Could someone with access to the current semester's Artemis course test the search performance when many submissions are shown? Currently, the code recreates all components for all submission entries on every character entered into the search field. This allocates many objects and re-layouts the container all the time. Maybe it's sufficiently performant, but if not, there are two options:

• Debounce the search field using Swing's Timer
• Use a real JList, which uses rubber-stamping. This would make the alignment between the different submission entries significantly harder, but could be very fast

[dfuchss]

I'll test it tomorrow

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud