Input types: 'default' value is not handled

[ashklianko]

Most of the built in types may have a 'default' value in their schema. This means that when creating a new content type that uses this input type, or when adding a new occurrence of the input, the default value to be set into the input field.

Notes:

• In input type schema 'default' value is defined as a separate variable, not in the input's config, but in requests for content schema it comes as a part of the config
• Previously backend was setting default values in a content when creating it, now it is going to be handled by UI part.

[ashklianko]

On hold until #4328 is done

[ashklianko]

Inputs with default values to handle:

• Checkbox
  "default - Use checked to check it, default is unchecked."
• Radiobutton
  "default is optional, and may be equal to one of the option values."
• Combobox
  "default is optional, and may be equal to one of the option values."
• Date
  "If value is set for an input, the Date picker will display "Set default" button for setting the default value with one click." - not only it, new occurrence must be rendered with default value preset
• DateTime
  Similar to date - preset value also
• Time
  Same as for date and time
• Double
  "default can be any double-precision floating-point number, with the dot character as decimal separator"
• Long
  "default can be any Integer number"
• Geopoint
  "default specifies a default string value for the GeoPoint, for example 51.5,-0.1"
• HtmlArea
  "default can contain any valid HTML elements, but tags must be correctly closed since the input type is defined inside an XML"
• TextArea
  "default specifies the default string for the TextArea"
• TextLine
  "default specifies the default string for the TextLine"
• OptionSet
  "default Set to true to pre-select one of the options"