Add grouping to Text, Image and Element Attribute selectors

Currently, only Grouped Selector can extract data from multiple elements into a single cell. Add a configuration option to Text, Image and Element Attribute selectors:

• Extraction type:

  • First element only (this is the current solution)

  • Join values (data from all elements will be joined in a single value)

    • separator (additional input to specify glue - ",")

  • Multiple columns (selector creates multiple columns instead of one. For example image1, image2, image3)

    • column count (number of generated columns specified upfront)