[TASK] Adapt gridelements support to newest gridelements

This change avoids setting colPos values when a gridelements drop zone value is detected (a relative "uid" containing an `x` character). Rather than attempting to set a colPos value this value is left untouched. What remains is clearing the `tx_flux_parent` and `tx_flux_column` fields to clear any relationship set by Flux, leaving it up to gridelements to handle the element from then on.
[BUGFIX] Do not return fields from a Sheet if field is inside Container

Close: #577
[BUGFIX] Enables flag icons for child content elements in page view language.
Merge pull request #634 from pixelmatseriks/workbench/flagIconsInBE

[BUGFIX] Enables flag icons for child content elements in page view lang...
[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