[TASK] Deprecate wizardTab and icon attributes on Form

This change:

* Marks as deprecated in code and rendered documentation, the arguments `wizardTab` and `icon` on `flux:form` in favour of the `options` attribute which is an array that can contain a `group` (equivalent of `wizardTab`) and an `icon` member.
* Removes properties on `FluidTYPO3\Flux\Form` but leaves in place getter and setter with deprecation logging, redirects storage to `options` class member.
* Introduces `OPTION_*` constants on `FluidTYPO3\Flux\Form` which define supported options. Other extensions are expected to either use what is provided here or introduce own constants (as constants in their own extension's namespace).
[BUGFIX] ConfigurationManager resolves bad PID from TS root record

This fixes a problem where page UID would be zero when Flux's overridden BackendConfigurationManager encountered cases where root page UID had to be resolved from an existing root TS record (as per default Extbase behavior - e.g. "use PID of primary root TS template"). Due to missing the `pid` field in query to select this TS record, the page UID would become zero (integer cast of a NULL value).

Problem was primarily present in backend modules based on Extbase and which do NOT use the page tree.
[TASK] Implement WorkspacesAwareRecordService in Grid Controller
Merge pull request #626 from NamelessCoder/deprecateoptions

[TASK] Deprecate wizardTab and icon attributes on Form
[BUGFIX] Update placeholder record values when saving

This change makes ContentService properly loop through the versioning chain (e.g. versions of versions of versions etc) until all records have been updated with the correct positioning (tx_flux_parent, tx_flux_column) values.
[TASK] Ship XSD schema file
[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