Sudomain support, register endpoint

[joepio]

• closes Wildcard subdomains #502
• closes Multi-tenancy #288
• closes sign-up / register endpoint: create a new Drive and a new Agent in one request #489
• closes Constrain new URLs #556
• relates to E-mail support #276
• relates to Tokens for Invites and Email confirmatin #544

TODO:

• Use new actix .full_uri() method instead of some hacky reconstruction. Will be added in 4.8 probably?
• Migrate trailing slash base URLs Migrate trailing slash base URLs #895
• Run this on some new domain, check if everything works over there
• Fix double path slash// in search results (and other places?)
• Find all the format!( occurences where we combine things to create a URL, replace with URL::join.
• Find a strategy to deal with going to a subdomain and losing your local settings (specifically your key!)
• Consider invite-only registration
• Fix all_resources check for include_external. Currently does not properly use subdomains.
• Add E2E test for registration
• Remove the existing new drive behavior
• Make sure users can't create resources on non-existing drives / subdomains. Constrain new URLs #556
• E-mail registration + token support E-mail support #276 Tokens for Invites and Email confirmatin #544
• /resetPubkey type of endpoint, in case you lose your private key
• Fix changelog (currently incorrectly changes previous releases)
• Tenantized querie Tenantized queries / collections. Scope queries by top level hierarchy. #570

PR Checklist:

• Link to related issue
• Add changelog entry linking to issue
• Added tests (if needed)
• (If new feature) added in description / readme

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[codecov-commenter]

Codecov Report

Merging #505 (93ab91e) into master (f5af18d) will decrease coverage by 1.77%.
Report is 2 commits behind head on master.
The diff coverage is 56.35%.

❗ Current head 93ab91e differs from pull request most recent head 7dac7b6. Consider uploading reports for the commit 7dac7b6 to get more accurate results

@@            Coverage Diff             @@
##           master     #505      +/-   ##
==========================================
- Coverage   66.12%   64.35%   -1.77%     
==========================================
  Files          73       79       +6     
  Lines        8200     8597     +397     
==========================================
+ Hits         5422     5533     +111     
- Misses       2778     3064     +286     

Files Changed	Coverage Δ
lib/src/authentication.rs	30.00% <0.00%> (ø)
lib/src/client.rs	21.97% <ø> (-7.88%)	⬇️
lib/src/db/migrations.rs	23.68% <0.00%> (ø)
lib/src/db/query_index.rs	95.61% <ø> (ø)
lib/src/hierarchy.rs	59.03% <0.00%> (-22.64%)	⬇️
lib/src/lib.rs	100.00% <ø> (ø)
lib/src/plugins/chatroom.rs	0.00% <ø> (ø)
lib/src/plugins/utils.rs	0.00% <0.00%> (ø)
lib/src/plugins/versioning.rs	71.11% <ø> (-0.63%)	⬇️
server/src/commit_monitor.rs	22.07% <ø> (ø)
... and 35 more

... and 10 files with indirect coverage changes