Upgrade to Maki 0.3

[martindale]

With the impending release of Maki 0.3, which adds a wide swath of new features, we should start planning porting converse over to use it, especially the new Component architecture.

Some challenges:

• moving from Semantic 1.x to 2.x
• converting UI controls to Components
• leveraging the new cryptographic identity available with <maki-identity /> (see also Cryptographic Identity #23)

It shouldn't require more than a weekend's worth of work, but let's keep it in mind as we finish up martindale/maki#120.