EUI: Reset CSS

[cjcenizal]

I've extracted the commits from #14948 which load the EUI CSS (thereby using its reset), and removing the Bootstrap, UI Framework, and custom reset CSS. Depends upon elastic/eui#153.

We'll need to complete the partial audit below and fix the regressions we find.

Partial audit

Here are a few of the visual regressions incurred by the CSS reset changes.

Notifications

• Notifications are missing padding around their edges, causing text to appear misaligned vertically and buttons to be flush against the top and bottom edges.

Timepicker

• Timepicker buttons don't have a pointer cursor when hovered, probably because they're a elements with no href attribute.
• The spacing also looks like it got tighter, causing the "collapse" button to get uncomfortably close to the "Absolute" button.

Query bar

• The "Add filter" button doesn't have a pointer cursor when hovered.

Discover

• The "Selected fields" label is too close to the index pattern title.
• The "Available fields" element become too short, causing the gear button on the right side to overflow.
• The link ("143" in the screenshot) is missing link styles.
• The vertical spacing of the values and progress bars looks too tight.

• When expanded, the labels are too close to the Available Fields inputs.

• In "Single document" view, the tabs lack pointer cursors when hovered, possibly because they're a elements without href attributes.

• Note: this applies to the tabs in an expanded row of the doc table, too.

Visualize

• The title is too close to the search bar in the Visualize Wizard.
• The sr-only accessibility class has been deleted, which means all elements previously hidden by it are now visible. We can fix this by replacing this class with euiScreenReaderOnly instead.

• The sidebar tabs lack pointer cursors when hovered, possibly because they're a elements without href attributes.

• The spacing between "Select bucket types" and the menu is too tight.

[cjcenizal]

Closing in favor of a branch on the original repo: https://github.com/elastic/kibana/tree/eui/reset-css

And this issue: #15315