Moving windows build to Github Actions

[algojack]

Moved it to build-test-windows here on Github.
Artifact gathering and upload are not currently working, since they seem to be cached files and we are not sure how useful those are. But if we can determine what exactly we need and for what purpose, we can add them back in.

Slack notifications for failed nightly builds added using slack webhook to #dev-alerts channel.
Travis integration removed.

Example slack message:

[codecov-commenter]

Codecov Report

Merging #3575 (41f7577) into master (6230dc5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3575      +/-   ##
==========================================
- Coverage   47.58%   47.58%   -0.01%     
==========================================
  Files         370      370              
  Lines       60118    60118              
==========================================
- Hits        28606    28605       -1     
- Misses      28198    28199       +1     
  Partials     3314     3314              

Impacted Files	Coverage Δ
ledger/blockqueue.go	82.18% <0.00%> (-2.88%)	⬇️
agreement/cryptoVerifier.go	75.17% <0.00%> (-2.13%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
ledger/acctupdates.go	65.58% <0.00%> (-1.15%)	⬇️
network/wsPeer.go	68.33% <0.00%> (-0.84%)	⬇️
data/transactions/verify/txn.go	44.44% <0.00%> (ø)
catchup/service.go	69.38% <0.00%> (+0.74%)	⬆️
cmd/tealdbg/debugger.go	73.86% <0.00%> (+1.00%)	⬆️
network/requestTracker.go	71.55% <0.00%> (+1.29%)	⬆️
ledger/tracker.go	75.75% <0.00%> (+1.29%)	⬆️
... and 2 more

---

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[onetechnical]

The python version is interesting, but otherwise looks alright to me.

[algojack]

The python version is interesting, but otherwise looks alright to me.

Removed, got it from circleci attempt to implement this, but seems we don't need it.