Enable/Disable or show/hide suggestions for a given browser tab (browser extension)

**What problem does this solve?**
When I am reading other people's documents in Google drive (for example), the Harper browser extension currently is enabled globally and will mark up the files even though you are not editing them. Many documents end up being 100% highlighted in different colors which is distracting when reading.

**Proposed Solution**
Users should have the capability either enable/disable harper on a given page/tab or show/hide the suggestions so that you can get an uncluttered reading view when you do not care about or can't take action on the issues on a page.

**Examples**
Here's the wikipedia page about Capybaras pasted into a google doc with Harper to show you how many things are highlighted.

**Component**
- [ ] Core engine
- [x] Plugin/Extension
- [ ] Other: _____

Start with the browser plugin/extension entry point and trace how suggestions are enabled and displayed for a tab. Clarify whether the completed behavior should be per-tab disablement, hiding suggestions, or both, then verify that changing one tab does not affect others and that Google Drive reading views can be uncluttered.

Written by the indexing model from the issue text.