MHQ Underbody to hold a Sonarsensor

This is an adaptation of the original underbody design by dohdohpub. Now it can hold an SRF10 sonar sensor that supports altitude hold and auto landing operations.

There are two different versions:

1) Sonar.stl - meant to be used with the origianl MHQ
2) SonarV2.stl - stretched version to fit the largwer MHQ2