Collective UI/UX rework/standardization tracking issue

[See original issue on GitLab](https://gitlab.com/BuildStream/buildstream/-/issues/1068)
In GitLab by [[Gitlab user @tlater]](https://gitlab.com/tlater) on Jul 5, 2019, 16:28

## Background

[//]: # (Provide a background or the root/source that justifies this task or action.)

There are a number of open UI/UX issues that will require breaking changes, and should therefore happen before BuildStream 2.0.

This issue is here to track progress on them, and ensure that we keep them in sight.

## Task description

[//]: # (Short summary of the action to be executed)

The following issues should be resolved as part of a UI/UX rework

### Blocking 2.0 milestone

* [x] #685
* [x] #773
* [x] #819
* [x] #1065
* [x] #1048
* [x] #1067
* [x] #822
* [x] #1349

### Not blocking 2.0 milestone

* [x] #345
* [ ] #771
* [ ] #422
* [ ] As part of this rework, we should also set our design principles for these things in stone - this should at least be documented in `CONTRIBUTING.rst`.

## Acceptance Criteria

[//]: # (Acceptance criteria should follow the S.M.A.R.T. principle https://en.wikipedia.org/wiki/SMART_criteria )

BuildStream's UI/UX is reworked and (hopefully ;)) shouldn't require future breaking changes.

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[//]: # (To review information about possible relevant labels for this issue please view the list of labels: https://gitlab.com/BuildStream/buildstream/labels)

Start by reviewing the linked tracking issues, especially unresolved #771 and #422, then inspect CONTRIBUTING.rst for where UI/UX design principles should be documented. The issue does not name a single code entry point; done means the remaining UI/UX work is resolved and the principles are documented without future breaking changes.

Written by the indexing model from the issue text.