linear view sticky title bar improvements

[psifertex]

#3453 is great but could use a few improvements:

• [x] adjust padding and styling slightly to more closely match graph view's version of the same
• [ ] ability to click and select arguments and have them highlighted just like the standard function prototype
• [ ] ability to copy/paste text from the header
• [ ] disable in single function view
• [ ] consider some way to quickly navigate to the top of the function using the sticky header

[negasora]

Padding and styling fixes done in 3.2.3896-dev

[op2786]

It's very useful feature if single function view is disabled. But if its enabled (which I always do) it looks very annoying, especially if function is not too long one. Actually I would prefer to use it in single function view but only if it can be turned into a format that will only show up when the main title bar is about fade off the view.