Script generator: rename "Line" to "Action" for consistency with buttons

[rerpha]

As an EMU instrument scientist/user I find it confusing that "Line" is the column name when i add an action. Someone who does not natively speak English may find this confusion.

Acceptance criteria

• "Line" in the script generator table column is renamed to "Action" to be consistent with the buttons that add/remove actions (rather than lines)

[rerpha]

PRs:

• IBEX - renaming line to action in script generator column names ibex_gui#1288
• Release notes - Ticket6434 #6435