[Qt] allow deletion of payment-requests in sendcoins

- this adds a delete button for insecure and secure payment requests in
  the sendcoins dialog
- it also enables the delete button even for single and empty entries, as
  this is much easier to handle and doesn't need to special case single
  entries
- big parts of the ui file were changed, because I copied the delete
  button and had to delete the layout too and created it from scratch
  (which seems to cleanup the rows and colums in the layout also, which is
  nice IMHO)
mutex debugging routines: LocksHeld() and AssertLockHeld()
Merge pull request #3306

84b695c [Qt] allow deletion of payment-requests in sendcoins (Philip Kaufmann)
Merge pull request #3329 from gavinandresen/syncdebug

mutex debugging routines: LocksHeld() and AssertLockHeld()
Make unit tests succeed with -DDEBUG_LOCKORDER
Fix a rare crash on Mac OS X, by removing a setFocus on the payTo field that was not necessary, as the field still receives focus without it.
Merge pull request #3339

bae6c7e Fix a rare crash on Mac OS X, by removing a setFocus on the payTo field that was not necessary, as the field still receives focus without it. (Ryan Niebur)
Lossless image optimization

less bytes, same images
Merge pull request #3341 from Need4Video/master

Lossless image optimization
Sanitize assert usage and refuse to compile with NDEBUG.

There were quite a few places where assert() was used with side effects,
 making operation with NDEBUG non-functional.  This commit fixes all the
 cases I know about, but also adds an  #error on NDEBUG because the code
 is untested without assertions and may still have vulnerabilities if
 used without assert.
Fix file hash verification error in deps-win32.yml

libpng was being sha256summed twice, and miniupnpc wasn't being checked at all.
Merge pull request #3344 from gmaxwell/assert_hazards

Sanitize assert usage and refuse to compile with NDEBUG.
Merge pull request #3345 from Michagogo/gitian-descriptor-deps-input-typo

Fix file hash verification error in deps-win32.yml