Some Python3 related fixes.
Merge pull request #21 from anntzer/py3fixes

Some Python3 related fixes.
Added Qt.loadUiType function for PySide
Added example of simple Designer usage.
Corrected mouse clicking on PlotCurveItem - now uses stroke outline instead of path shape
Added 'width' argument to PlotCurveItem.setClickable()
Merge branch 'plot_curve_picking' into develop
Fixes related to CSV exporter:
  - CSV headers include data names, if available
  - Exporter correctly handles items with no data
  - pg.plot() avoids creating empty data item
  - removed call to reduce() from exporter; not available in python 3
  - Gave .name() methods to PlotDataItem, PlotCurveItem, and ScatterPlotItem
Fix examples/hdf5.py to work properly with --test
pyqtgraph, .exporters, and .opengl now use static imports
python3 fix
Flowchart:
* Replaced dynamic imports with static
* Added NodeLibrary allowing multiple customized collections of Node types
python 3 fixes
Merge branch 'static_imports' into develop

No more dynamic imports; pg uses static imports throughout.
Flowcharts and exporters use plugin systems
Switching to relative imports to allow pyqtgraph to be imported under other names.

finished top-level files and graphicsItems
updated widgets
console, graphicsscene, and 2nd-level graphicsitems
exporters, multiprocess, opengl
flowchart, canvas
dockarea, imageview, metaarray
.ui files
rebuild UI files