bump version to 1.2.0

Handle closing/opening of LCU

Makes LCU Explorer more robust in the face of opening/closing/reopening
of the LCU client, and slightly faster. FE keeps all the state in
`useState` calls which allow the Swagger UI, OpenAPI spec JSON, and the
LCU credentials to load (or unload/reload) in any order. A basic plugin
updates the Swagger UI on changes.

When not connected to the LCU the endpoints still show up but the "Try
It Out" buttons are hidden.

fix Mingwei's gh link