feature: notifications

[nick1udwig]

1. Notify about a vote period opening if user has a lock active (i.e. has voting power that can vote in that proposal)
2. Notify about a proposal pre-voting-delay period ending in 48 hours
3. Notify about a new proposal being made
4. Settings page to toggle on/off these notifs

Practically this looks like:

1. When proposal is created, determine when pre-voting-delay period ends and set a timer for 48 hours before then; if user wants notifs on "proposal made", notif
2. When app starts (i.e. on reboot), check all proposals and set timers for 48 hours before pre-voting delay ends if that is in future
3. When 48-hour-timer pops, check if user wants notif, if yes, notif
4. When a voting period opens, if user has lock active and wants notif, notif

Defaults probably look like

1. Notif on vote period opening: yes
2. notif 48 hours: yes
3. Notif new: no

Extra credit: only notif during user's waking hours (i.e. timer logic should be used to delay notifs till we think user is awake)