close dropdown on mouse leave and add hover effect dropdown elements

[hasanheroglu]

Closes #137 Closes #39

[egekorkan]

So this is definitely better than before but not fixing the issues completely. I have tested in Linux.

• clicking + for add an element and then clicking anywhere but the buttons closes the pop-up. Clicking on one of the pop-up items opens the new window but does not close the pop-ups, no matter where I click. Then, when I create a Thing or folder or if I cancel, I can close the pop-up only by pressing on + again.
• Same behavior if I click on the three dots next to folders on the sidebar
• In performance tab, the same behavior happens with any item that can have a pop up such as type, delay, confidence level