BibEditMulti: multiple improvements and fixes

• When changing condition subfield of Delete action, change was not applied. (fixes #1146)

• After selecting the type of action in the dropdown, the first subfield action opens automatically. (fixes #1147)

• Moves the "Define new subfield action" to the left. (fixes #1148)

• Extends 'Apply only to specific field instances' to apply actions when a subfield does not exist. (fixes #1130)

• Optimizes the time of preview generation. (fixes #1149)

• Only modifies the results with checkboxes checked (fixes #1156)

• When updating a field, there is now possibility to add more fields for "replace substring" conditions (fixes #1158)

• Uses regular expression instead of replace function