Add ability to create empty presentation and spreadsheet.
To create an empty document in odf.OdfContainer, the type of the document should be passed. If a string is passed, it is interpreted as url and an attempt is made to load a document from that url.
Merge pull request #558 from vandenoever/odp

Add ability to create empty presentation and spreadsheet.
Add ability to create odp files in the layout tests.
Only a dummy tests without checks is added so far.
Make code more readable with a isText variable.
Merge pull request #561 from vandenoever/frame03

Add ability to create odp files in the layout tests.
Clean-up unnecessary variable name and associated API dox
Ensure merged paragraph style names are well defined

Though getAttributeNS is now standardised as of HTML4 to always return
null, according to MDN documentation browsers can return a variety of
values for a non-present attribute (generally null or ""). Update the
logic in TextController to always use "" for the merged style name as
the inline comment suggests is the expected behaviour.
Remove obsolete paragraph merge logic

As destination & source now never change, there is no need to re-
position the source paragraph. The source paragraph will now always be
checked for possible removal.
Merge pull request #562 from peitschie/getattr-fix

Ensure merged paragraph style names are well defined
Deal explicitely with parentless automatic styles

also stop assuming that automatic styles can have other automatic styles
as parent
Built-in default values for optional attrs fo:text-indent and text:min-label-distance
Fix StepsCache's getNodeId() to always return a string
Fix getAttributeNS related comment in RelaxNG2's validateAttribute()
Make parsing methods of odf.OdfUtils deal with undefined & null values
Fix exception on  masterPageName being null in odf.StyleCache.masterPage()
Do not pass null to odf.Formatting.getMasterPageElement()
deal with possible not existing xlink:href attribute in OdfUtils.getHyperlinkTarget

as this is in a public method with no other check if the passed element
is a proper <text:a> element, better be safe then sorry
Make parsing methods of odf.StyleParseUtils deal with undefined & null values
attribute style:display-name is only optional, use style:name as fallback for display
Make odf.StyleParseUtils' lengthInPx() deal with undefined & null values