Update providers.json

Added MX records for Yahoo mail.
Merge pull request #666 from rlaferla/master

Update providers.json
Fixed #671: workaround bad message encoding
Gitignore file has been improved.
Merge pull request #672 from maximkhatskevich/master

Gitignore file has been improved.
deletion of ending characters made easier
Fixed type conversion
Fixed build of mailcore2 for iOS 7.1
Made very short display string even shorter