Allow browsing without creating account similar to Mastodon web

[d4f5409d]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. If somebody just wanted to check out the Fediverse, Mastodon and they didn't want to create an account, they could use Megalodon to browse it.

Describe the solution you'd like
A clear and concise description of what you want to happen.
All features should work in no account / incognito mode except which require an account. When a user wants to favorite, or follow someone, a popup windows should open to let them register.

Describe alternatives you've considered
If applicable: a clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

This can be connected to #222