🎨 Visual updates

Few small (but long overdue) update to improve usability:

New relationship type selector

Rebuilt this component from scratch. Previously it was using browser default select element which limited style customization, and resulted in awkward sizes when the diagram is zoomed.

New import wizard

Previous import offered multiple options for the different sources. This made sense back then when we envisioned for diagrams in DrawSQL to be 'DBMS agnostic', so users can create generic diagrams, and import/export them in any DBMS that they like.

While that's nice to have, however, we've learnt over time that for most apps out there switching the DBMS happens quite rarely. Making the editor be DBMS-agnostic had some limitations too - the major one that was causing headaches was that there wasn't a direct 1-1 mapping of column datatypes between the different DBMS. We tried a few different designs on the datatype selector to cater for this, but were not satisfied and felt like they were still unsatisfactory in terms of usability.

We're leaning towards an overhaul so that each diagram has a distinct DBMS selected. Revamping this import wizard is the first step in that direction.