Emulator doc should contain all emulator known issues and troubleshootings

Emulator related known issues and troubleshooting items are currently mainly under the Qt for Device Creation documentation. They should be found from the emulator documentation too (easier for the end users to find them).

The current emulator documentation already contains a known issues page (http://doc.qt.io/emulator/emulator-known-issues.html) so all the emulator known issues from  the DC documentation can be added there too. A new page for emulator troubleshooting needs to be created.