Logic cleanup, new confirmation/submit button/edit GF entry functionality

Some logic clean up for the main Pods_GF::__construct, moving into _gf_pre_render instead

Switching read_only to static handling for on-the-fly setting; Pods GF UI updates and fixes

Added new 'edit' option to enable editing leads instead of inserting them

Added new 'submit_button' option to allow for overriding the submit button per action (for when you're using the same form in multiple actions for workflow, very handy when used in combination with 'read_only')

Added new 'confirmation' option to allow for overriding the confirmation text/redirect per action (for when you're using the same form in multiple actions for workflow, very handy when used in combination with 'read_only')