UI updates

• Allow selecting multiple markers/lines by holding Shift and drawing a box.
• Allow deleting multiple markers/lines at once (see handle multiple objects in the docs).
• Add loading spinners to a lot of buttons to indicate when an action is still running.

Bugfixes

• Fix custom import dialog when multiple files are open.
• Fix lines being shown incorrectly or not at all in some circumstances.

Technical changes

• Publish facilmap-utils, facilmap-types and facilmap-server packages transpiled to JS.
• Allow running facilmap-server straight from NPM (see docs).