[BUGFIX] Use extension signature, not extension key, as container scope

The extension key may contain underscores; these will not be present in the TypoScript. Example: extension key "my_ext" becomes "plugin.tx_myext" in TypoScript.
[FEATURE] Add shortcut method to fetch View configuration for extension by name
[FEATURE] Error handling convention with toggle for behaviour

This adds a default errorAction on Flux controllers and attempts to capture errors and improve the normal Exception-based error feedback - in order to better report issues arising from missing configuration, missing paths, missing files, invalid options, bad Flux form structure etc.
[TASK] Implement a limited back trace for custom error views
[TASK] Do not cache per-page setup to files

The TS is already cached this way - processing is fairly light and the configuration is only processed once per page (or retrieved from internal cache).
[TASK] Remove unnecessary JSON Service previously ported from FED
[TASK] Rename Service / Debug -> Service / DebugService
[TASK] Rename Service / Grid -> Service / GridService
[FEATURE] Master Flux Service

This new Service contains all methods from the old methods, rationalised and cleaned up.

Transformation of FlexForm data is temporarily disabled.
[TASK] Rename Service / Content -> Service / ContentService
[TASK] Remove Service / FlexForm
[TASK] Remove Service / GridService
[TASK] Remove Service / Configuration
[TASK] Remove Provider / ConfigurationService
[TASK] Switch to renamed Services, remove usage of removed Services
[TASK] Get extension key from Provider instead of Request

This allows the Provider to have a say in which extension context is used when rendering - while the AbstractFluxController is agnostic about this, ConfigurationProviders are perfectly okay being allowed to override extension context.
[DOC] Add missing variable type declaration
[TASK] Allow Exposed View to read extension key from setup if not given as argument

This can shorten calls to the method (given that some path collections already contain the extensionKey setup parameter) while still letting the extensionName parameter override any defined configuration. In many cases the extensionName parameter would have been read from the same setup that contains the extensionKey parameter.
[TASK] Make ExposedTemplateView read config same as ExposedStandaloneView
[TASK] Clean up a few default value returns in FluxService