Fixes#295
If a row should be written with a custom style, the handling of empty cells should change.
Instead of being skipped entirely, empty cells will be applied the custom style, if this style has custom background color or borders.
If not, then the cell definition can still be skipped.
* Fix#276, some general refinement
* Failing test #267
* Fixed shared border definitions across different styles #267
* Fix finding the correct borderId
When a cell contains multiple text nodes, the cell value is currently obtained by concatenating the value of each text node.
Instead, values should still be concatenated but a space should be added in between.
When reading spreadsheets, Spout should be able to return formatted dates, as shown when opened with Excel for instance.
It currently only returns DateTime/DateInterval objects, making it impossible to read + write, as the Writer does not accept objects.
Instead of relying on the ID, sheets should be retrieved in the order they appear in the file.
Workbook.xml describes the correct order.
This allows the reader to read data in the correct order when sheets have been manually moved after creation.
This fixes issues when something went wrong on reader/writer init and the developer wants to close the reader/writer.
The file handle may not be defined so we need to add a check for it, before actually using it.
The value passed into the format() function is coming from an XML file and has never been coerced.
Therefore, when checking is_int($value), the check always returns false - because it's a string.
Changing the check fixes the issue and Spout now correctly parses large numbers.
Some software generate [Content_Types].xml file with sheets definition in random order.
Instead of having the first sheet (id = 1) defined first, it may be defined in 3rd position.
Therefore, to read the file in the correct order, sheets order need to be fixed.
The ZipHelper interface is now more generic and allow single files to be added.
It supports adding uncompressed files (for PHP7+), which is required to have the mime detection magic work with ODS files.
Also fixed a few issues with the created ODS file (thanks to https://odf-validator.rhcloud.com/)
Heuristics to detect proper mime type for XLSX files expect to see
certain files at the beginning of the XLSX archive. The order in which
the XML files are added therefore matters.
Specifically, "[Content_Types].xml" should be added first, followed by the
files located in the "xl" folder (at least 1 file).
