Updating mechanism for mainnet

[nkryuchkov]

NOTE: After merging this PR, all git tags and GitHub releases should be removed because they exist for testing purposes.

Did you run make format && make check? yes

Fixes #129
Fixes #141

It should be merged simultaneously with https://github.com/SkycoinPro/skywire-services/pull/84.

Changes:

• Implement skywire-visor and skywire-cli binary files update via the hypervisor
• Change GET /visors/{pk}/restart to POST /visors/{pk}/restart
• Setup goreleaser for skywire-visor and skywire-cli

How to test this PR:

1. Comment out the VERSION := $(shell git describe) line in Makefile
2. Add a new line below it: VERSION := 0.1.0
3. Run the generic integration environment
4. Go to VisorA pane
5. Make an HTTP POST request to localhost:8080/api/visors/024ec47420176680816e0406250e7156465e4531f5b26057c9f6297bb0303558c7/update
6. Check if there are no errors in VisorA pane and VisorA is restarted successfully and works. Apps should also work. Versions of all binaries in their output should be updated.
7. Check if the HTTP response status is 200 and body is true
8. Go to shell pane
9. Check if skywire-visor, skywire-cli and VisorA apps binaries are updated and work (e.g. using ls -lah ./bin)
10. Check if files/directories from logs from VisorA saying Removing file ... are removed.
11. Note that in fact, an old version of binaries is uploaded to the last GitHub release. GitHub releases need a clean-up.

[Darkren]

Other than these small things, it is a really great job!

[Kifen]

Nice work

[jdknives]

Works well in the integration env. Really good job man! Would like to give that another test outside of the integration env as soon as test deployment is stable again though.

[jdknives]

Also, we need to add support for updating appliations.

[jdknives]

Works like a charm. 👑