Ability to create post without being in community feed

[micahmo]

Pull Request Description

This PR adds support for initiating a new post without an existing community context (i.e., from home feed) and allowing the user to select any community to post to.

Note: This could lead into a feature where we can share any link to Thunder and create a new post from it, as suggested in #639.

Note: Technically, this change allows you to initiate a new post within a given community and then change to a different target community. I don't think this is necessarily a bad thing though.

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

qemu-system-x86_64_Z3vwdUU01y.mp4

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

LGTM!

One feature that we could add (doesn't have to be in this PR of course) would be to have a pre-generated list of suggestions based on the communities that the user is subscribed to. This way, the user can easily select one of their subscribed communities to post to rather than having to type them in!

We do keep a list of the user's subscriptions in AccountState so this could be used in this case to reduce further API calls.

[micahmo]

One feature that we could add (doesn't have to be in this PR of course) would be to have a pre-generated list of suggestions based on the communities that the user is subscribed to.

Good idea!! Done in e659566.

qemu-system-x86_64_hpDWn5EP56.mp4

[hjiangsu]

Looks good! I just realized I made a typo with subscriptions (should be subscriptions instead of subsciptions)