[MU3] Fix macOS dmg name, fix macOS dmg window height, update version number

[cbjeukendrup]

• Fixed macOS dmg name
  The name of the downloaded dmg was okay, but the name of the volume that is mounted when you open the dmg was wrong:
  
  I fixed it in such way that it will match what was intended previously. If we ever want to change it, that can be done very easily now.

• Fixed macOS dmg window height
  Make the full background image visible, by taking the height of the window title bar into account.
  

• Update version number
  To 3.6.2. (I assumed that would be desired, or isn't it?)

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• I made sure the commit message title starts with "fix #424242:" if there is a related issue
• I created the test (mtest, vtest, script test) to verify the changes I made

[Jojo-Schmitz]

Would a change equivalent to 0ef97b5#diff-9e7722ca57674a1f6b12e1b419c1cd4918ab641dd58b60127de7427417ade066L3-R3 be needed here too?

(Sorry, a tad late...)