Added a new setting for switching between "smooth scrolling, minor issues" and "non-smooth scrolling, no issues", set to smooth scrolling by default. The second option fixes a number of issues where Mouse Tweaks seemingly scrolls "through" another mod's GUI (namely JEI): 1, 2, 3. Unfortunately, enabling the second option also makes the item scrolling a little non-smooth. Considering that the aforementioned issues require rather specific conditions to trigger and aren't very impactful, while scrolling items is something you do all the time and want the experience to be as good as possible, the setting was left at "smooth scrolling" by default. Huge thanks to @mezz for contributing the fix and explaining the underlying input mechanics.
Fixed Mouse Tweaks clicking "through" some mods' GUIs (namely JEI): read above for details. The fix is active regardless of the smooth/non-smooth scrolling setting value.
Added tooltips to all settings in the Forge Mod Options menu.
Bumped the required Java version to 8. If this is a problem, please open an issue, it's possible to bring it back down to 6.