Bitcoin-Qt: save and restore position of debug window

[Diapolo]

• move the code for saving and restoring window positions from BitcoinGUI
  to GUIUtil, make it more generic and also use it for saving/restoring
  debug window positions

We also could allow this for all other dialogs, if we want, but that is currently not the goal of this pull.

[laanwj]

I'd prefer factoring out this code to utility functions or an utility class, instead of just copying it.

[Diapolo]

@laanwj That IS a good idea, thanks.

[Diapolo]

@laanwj Can you take another look :)?

[BitcoinPullTester]

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[laanwj]

ACK on code changes, haven't yet tested

[Diapolo]

Updated commit-msg and also removed and include from bitcoingui.cpp.

[BitcoinPullTester]

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/c431e9f1f03023d216db0ff48d3d598e705c97f9 for binaries and test log.
This test script verifies pulls every time they are updated. It, however, dies sometimes and fails to test properly. If you are waiting on a test, please check timestamps to verify that the test.log is moving at http://jenkins.bluematt.me/pull-tester/current/
Contact BlueMatt on freenode if something looks broken.

[Diapolo]

@laanwj Did you test the patch yet?

[gavinandresen]

ACK: tested on OSX.