fix: use Status.WARN instead of ERROR

[azu]

If ERROR is set to ERROR, the OUTPUT panel opens, so use WARNING instead.

This PR changes the behaviour when opening a project without textlint installed.

BEFORE

vscode-textlint was ERROR

AFTER

vscode-textlint will be WARNNING

fix #66
cc @taichi

[piranna]

Can this be merged? I'm facing the same issue.

[piranna]

Any update on this? How can we move it forward besides remove the extension? This issue is very annoying... :-(

[piranna]

After reviewing this, I think in fact the error is legitim: the textlint executable is not being found, that can be considered that's actually an error. Point is, if there's no .textlint file, that's a totally acceptable use case that should show a warning instead, but the executable should not be looked at all. So I think this PR should address that:

1. look for the .textlint file, if it doesn't exists, show a warning a do anything else
2. look for the textlint executable, if it doesn't exists, show an error as currently does

Our princess is in another castle... :-)