Expandable space for commit messages

I find the space allocated for writing commit messages is much too small.

I can't find any part of the UI to "grab" so I can expand the area for the commit message. Neither have I been able to find a relevant preference.

I'd prefer that:

• I could "grab" the bottom of the text box that contains the commit message and drag it to expand the area.
  
  
• The GUI remembered my preference from commit to commit.