fix(dashspend): robust Explore DB v3 upgrade

[Syn-McJ]

Issue being fixed or feature implemented

• If the app didn't update to v3 Explore database prior to the user opening the Explore feature, the app will crash due to a schema mismatch.

What was done?

• Check the DB schema, don't connect if old
• Wait for new DB download
• Show "data is syncing" notification
• Reload search results once DB is ready

How Has This Been Tested?

QA

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[pankcuf]

LGTM