Unbreak master page rendering in ODPs.

Restricted the `z-index: 1` hack for draw|frame to
frames within office|text, since it was intended for
ODTs in the first place.
Merge pull request #531 from adityab/zframe

Unbreak master page rendering in ODPs.
Add test for frame position.
Add a helper function to get the bounding rectangle for an ODF page.
Improve positioning of frame that relative to page.
Add type that is a union of ClientRect and a struct with the same members.
This makes is possible to use them interchangeably.
In older browsers, positioning is only allowed on whole pixels.
The positioning test should set the allowed error higher in such browsers.
Add more supported length units.
And add a bit of documentation.
Check for null return value for getBoundingClientRect.
Slight clarification of exception.
Add tests with draw:frame directly in office:text.
This requires position: relative in office|text to get the frame positioned properly.
Simplify layout tests by having common styles.
Fix positioning for horizontal-pos="left" and vertical-pos="top".
Code cleanup and add a test for anchor="as-char".
Move getStyleElement from odf.Formatting to odf.StyleInfo.
Also add description to some functions and make convertToPx clearer.
Fix positioning of frames in ODP files.
This fixes a regression. In ODP, the location of frames is relative to the top and left of the page, but this is not explicitly specified in the styles.
Add test for frame position.
Add a helper function to get the bounding rectangle for an ODF page.
Improve positioning of frame that relative to page.
Add more supported length units.
And add a bit of documentation.
Remove type odf.OdfRect.
It is not needed any more. No call to getPageRect modifies the resulting ClientRect.
Fix positioning for horizontal-pos="left" and vertical-pos="top".
Add test for frame position.
Add a helper function to get the bounding rectangle for an ODF page.