Two existing themes retain their styling, though the cssjs now
checks whether a few properties are set to custom: true on the
current style, if so passes the value, otherwise returns the
existing default

Ref: #1198

My commit message body

Ref: #1198

Inconsistent UX can cause problems and unhappy users

Ref: #1198

New theme is a clean blank white one, replaces background colors and adds solid black borders.

Ref: #1198

remix-plugin 0.0.5 integration

[WIP] Integrate remix-plugin 0.0.3

Refactor udapp, run tab and related components