Feat #59 Option to allow tabbed pane separator to take full height

[smileatom]

No description provided.

[DevCharly]

@smileatom many thanks for the PR.

I've merged it with minor modifications:

• removed unused FlatClientProperties.TABBED_PANE_TAB_SEPARATORS_FULL_HEIGHT
• moved tabSeparatorsFullHeight next to showTabSeparators
• added to change log

[DevCharly]

BTW to update your repos master branch to latest FlatLaf master branch, it is not optimal to use GitHub pull requests.

Better:

1. add https://github.com/JFormDesigner/FlatLaf as second remote to your local git repo with the name upstream
2. fetch from upstream to your local repo
3. do fast-forward merge upstream/master to your local master
4. push commits to origin (your fork on github)

Here is a more detailed description:
https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/syncing-a-fork