AppVeyor: prevent unnecessary builds

[tooomm]

Short roundup of the initial problem

AppVeyor CI always started builds, also on completely unrelated changes.

What will change with this Pull Request?

• prevent builds on .md changes, like a README.md update
• prevent builds on config changes for other services, like travis, transifex, gitlab or github

Results in faster check marks for quicker merging. Also, important builds don't queue up and have to wait for such unrelated build to finish.
For example, travis is building this change to a appveyor config file, a total waste and delay!

Am I correct, that we don't want AppVeyor to build changes made in the webclient as well?
Did I miss anything?

---

This also removes the qt5 extension for the windows builds. We don't use such a tag for our macOS and Linux builds.
Sadly this is needed as of now:

Cockatrice/cockatrice/src/releasechannel.cpp

Lines 59 to 68 in ff6b0f8

	if (wordSize == "llp64") {
	arch = "win64";
	devSnapshotEnd = "-x86_64_qt5";
	} else if (wordSize == "ilp32") {
	arch = "win32";
	devSnapshotEnd = "-x86_qt5";
	} else {
	qWarning() << "Error checking for upgrade version: wordSize is" << wordSize;
	return false;
	}

We need a workaround for this to finally remove it in future versions. At best before releasing a new version. Just add an additional check for -x86_64 and -x86 without qt5 for the transition period?

[tooomm]

Tested and working with changes to these files:

• .github/CONTRIBUTING.md
• .tx/config
• .travis.yml
• .dockerignore
• README.md

All of these correctly didn't trigger AppVeyor builds! 👍
The only untested rule is a (nested) change in webclient/ folder, all others are ok.

Cancelled all the pending macOS builds on travis. Linux builds fine for sure and we don't want to wait several hours for all of these to finish. 😆

[tooomm]

There seems to be a problem with the GitHub status check and how it expects results for Required builds.
It looks like this makes GitHub expect these builds to always happen, therefore the "waiting for pending" status unrelated if there is or going to be a build at all.
And we successfully skip a AppVeyor build here - so no status response from them...

This looks to be a very minor issue, given the benefit.
Admins can still merge such PR's, or we could loosen the Required condition and make it a general policy instead a platform controlled enforcement.
But I'm also in contact with AppVeyor support to find a solution.

[ctrlaltca]

This seems to work: the last build has been skipped.

[tooomm]

Linking AppVeyor support ticket and discussion: appveyor/ci#1848