Replace some core png icons with svgs

[laryn]

The drag and autocomplete throbber icons should be replaced with SVG alternatives:

[laryn]

Work in progress: #122

CleanShot.2024-04-03.at.10.02.19.mp4

[laryn]

[laryn]

Other possibilities:

• contextual gear
• dashboard external link icon

• list options + and -

• installer icons (note doubled up 'x' and the checkmark for "remove", which should be an 'x'):

• layout block dragger

Double check:

• messages
• views UI

[laryn]

Work continues; reopening.