Double quote support for SUMIF()

SUMIF() should handle double quotes properly in both criteria and
cells values. This is especially useful when we need to compare string
containing themselve double quote(s).
Travis: test also against PHP 5.5
General: Fix to calculation properties for Excel2007 so that the opening application will only recalculate on load if it's actually required
General: Modified Excel2007 Writer to default preCalculateFormulas to false
         Note that autosize columns will still recalculate affected formulae internally
Case-sensitivity fix
Added page header and footer examples to print options demo script
Added an isFormula() method to the cell object
Fixed silly missing ; typo
Eliminate some code duplication
Fixed problem in Excel 2007 reader with headers and footers containing multiple images. All images were substituted with the first one.
Updated data validation example to show a list derived from data in the worksheet rather than from a comma-separated string
Number format mask test for dates: test for "General" format should be case-insensitive, and scientific format mask shouldn't return a positive for date
Trap for scientific format masks with "0" or "#" before the "E"
Bugfix: (tavoarcila) Work Item GH-259 - Bug fix reading Open Office files
Merge pull request #244 from Slamdunk/patch-1

Travis: test also against PHP 5.5
Merge pull request #256 from trik/develop

Excel 2007 fail with headers and footers containing multiple images
Merge pull request #228 from PowerKiKi/patch-sumif

Double quote support for SUMIF()
Merge branch 'develop' of https://github.com/PHPOffice/PHPExcel into develop