gaby: template de-duplication and UI fixes

[tatianab]

Unify common templates where possible.

UI fixes:

• remove old result box when a new query is made

[gopherbot]

Change https://go.dev/cl/626535 mentions this issue: internal/gaby: refactor templates and pages

[gopherbot]

Change https://go.dev/cl/631655 mentions this issue: internal/gaby: clear old result when new query is made