[BUGFIX] Incorrect child content in page language view

Updated condition to include all localizations of page. Makes child content elements visible in both columns in page language view. Fixes #630. The initializeLanguages makes it possible to enable flag icons from ContentElementViewHelper.
Merge pull request #633 from pixelmatseriks/workbench/bugfix630

[BUGFIX] Updated condition and added initializeLanguages.
[BUGFIX] Incorrect record manipulation on copy

This change rewrites the logic of record copying inside ContentService, bringing it to a properly commented and revised state.

Tested working after this change:

No misbehaviors detected in standard language after applying this patch.

References: #573
[FEATURE] Returning of template source in Provider

This change implements a new method `getTemplateSource($row)` which allows a Provider to return the source of a template, which in turn will allow implementations to operate without a template file.
[FEATURE] Let View support setting template source

This change enables outside setting of template source for a Fluid View, the template source string is then used instead of reading the contents of a file, which in turn allows the View to be operated without a template file.
[TASK] Test for source getter and setter on Exposed View
Merge pull request #637 from NamelessCoder/copying

[BUGFIX] Incorrect record manipulation on copy
[TASK] Adjust Exposed View to better function with source

Avoids getTemplatePathAndFilename in cases where local source is given.
[TASK] Adjust AbstractProvider to better function with source