BUrlRequest: fix various issues

* Remove unused headers interface from BUrlProtocol
* Change confusing function names
* Style fixes and whitespace cleanup
Minor BPath doc cleanups.

* Implements BFlattenable::method not overrides, pure virtual.
* Tense of return values should be past.
Forgot this, add a period
Update Web+ find bar close button.

* Put the button on the left and label it with × to indicate close.
* Make the button just wide enough to fit the label. Tested with
  font sizes 8pt to 18pt.
Use default spacing for find bar controls
Lock about window before deleting it on destruction

This fixes #9543
Add methods to get and set the name, version, and icon
Close about window on escape
Switch about window to current workspace if hidden.
Move Deskbar prefs window to current workspace if hidden
Update Tracker prefs window workspace behavior.

Basically make the Tracker preferences window work like most other
windows do as far as workspaces go.

Opens on your current workspace. If you switch workspaces then go
into Deskbar and select Tracker Preferences it will switch to
the workspace that already has the window open. If you close the
window, switch workspaces and then select preferences it will move
the window to your current workspace and show it.

This is similar to the fix for the same problem on the Deskbar
preferences window and for the same reason: the window gets hidden
when you close it, not actually deleted so we need to do a bit more
work to get the window to behave with workspaces. Hiding instead of
deleting the window allows us to remember where you were when you
closed the window, what tab you were on, what control had focus, etc.

Fixes #8000
Update Deskbar to use menu text and selected menu text color prefs.

... in a couple of places where colors where being hardcoded.

Fixes #9119
Fix init.problem in setmime MimeAttribute ctor

* additional check for empty attribute values introduced;
* implemented copy-ctor and assignment operator for MimeAttribute;
* added missed initialization of parameters in the "UserArgs"
  MimeAttribute ctor;
* Fixes #9444.