fix# 306180: Adding notes to a tuplet now adds them with respect to t…

[blackears]

Resolves: https://musescore.org/en/node/306180

Adding notes to a tuplet in piano roll editor now adds them with respect to the tuplet's space.

Adding a method to Fraction to return the inverse.

Updating header comment in tuplet.h

• 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

[anatoly-os]

Let's postpone further improvements for the PRE to the MU 4. Please rebase this and other PRs onto master.

[blackears]

Was talking with chat - they were saying that the UI is being rewritten and that the 3.x branch is pretty well a dead end at this point. So my changes cannot be made to the master branch because it is really just acting as a placeholder right now and is going to be completely replaced.

The four PRs I submitted work with the 3.x PRE and will provide some bugfixes and functionality. Since they cannot be applied to the master, would it still be possible to apply them to 3.x just to leave this branch in the best possible state?