VCS: Show message box on timeouts/Add SSH prompt.

- Use message boxes on timeouts.
- Add a configuration for a graphical SSH password prompt binary with
defaults
- Launch commands that require authentification with no terminal on UNIX
and environment variable SSH_ASKPASS set accordingly.
- First attempt at introduce a common function to synchronously run VCS
commands in base plugin with flags.
- Use standard execution log entries in all VCS plugins (outputwindow).

src/plugins/vcsbase/vcsbasesubmiteditor.cpp

@@ -584,7 +584,7 @@ bool VCSBaseSubmitEditor::runSubmitMessageCheckScript(const QString &checkScript
     }
     QByteArray stdOutData;
     QByteArray stdErrData;
-    if (!Utils::SynchronousProcess::readDataFromProcess(checkProcess, 30000, &stdOutData, &stdErrData)) {
+    if (!Utils::SynchronousProcess::readDataFromProcess(checkProcess, 30000, &stdOutData, &stdErrData, false)) {
         Utils::SynchronousProcess::stopProcess(checkProcess);
         *errorMessage = tr("The check script '%1' timed out.").arg(checkScript);
         return false;