No longer buttons so switch to Rectangle for cleaner Qml

Waiting for real fix to put back. Issue #1275

Fix for Issue #1255

Also fixed a typo (copy/paste error) in the TCP link settings loading where it was using the UDP port as the default value instead of the TCP port.

changed criticalMessageBoxOnMainThread(const QString& title, const QString& msg) to QGCMessageBox::warning

Switched to new. I’ve seen this before with other Qt classes and have
had to change the usage in the same way.

I understand the intent when this was first created but nobody is using it and it no longer fits the context. If and when a need to abstract the serial link comes back, we can revisit this.

Removed "Clear Text" context menu from roll down dialog
Fixed "Clear Text" context menu in Info Dialog (renamed to "Clear Messages" in the process)

Also converted qDebug statements to logging category

Shrunk the Message drop down dialog a bit.
Made the Message drop down dialog slightly transparent.

Replace QMessageBox::warning by QGCApplication::criticalMessageBoxOnMainThread and removed unnecessary copying action

Added to ". Please provide a different file name to save to." to the error dialog