Stabilize and polish Outbound translation UI

[andrenatal]

• Why takes a long time to load and inject the form widget into the page.
• The form widget should always have the topmost z-index. Some STRs here: Form translation component should be always on top #16
• Polished UI with some usage instructions
• Translations are broken in the latest messaging batched mechanism
• Add dynamic scrolling to the backtranslation textarea
• Display the widget when input texts are selected besides only textareas
• Listen to mutations that add new editable forms to the Dom after the first scan (Form translation dialogues hidden behind page's modal veil #12). Basically unhook to the mutation listener on inpage and have its own for OT looking for what's pertinent.
• Outbound Translation messages to the translation worker should have top priority.
• Error when widget loses focus: Error when outbound translation widget lose focus #57
• Rebase