This PR adds support for cell alignment for XLSX and ODS files.
You can now align the content of the cells this way:
```
use Box\Spout\Common\Entity\Style\CellAlignment;
use Box\Spout\Writer\Common\Creator\Style\StyleBuilder;
$style = (new StyleBuilder())
->setCellAlignment(CellAlignment::RIGHT)
->build();
...
```
Possible cell alignments are: LEFT, RIGHT, CENTER and JUSTIFY.
This commit introduces Row and Cell entities, that will replace the arrays passed in previously.
It also adds support for Cell styling (instead of Row styling only).
* Refactor readers to get a proper DI
Similar to what was done with writers, readers also needed to be updated to match the new way of doing things.
This commits promotes a better DI (factories, injection through constructors).
* Escapers should not be singletons
Instead, they should be proper object that can be injected where needed.
This will improve the management of options and simplify some methods' signatures.
This commit will also help moving the code to a better state regarding Dependency Injection.
