Avoid manual handling of icons in request field list items
* Use `PurpleKeyValuePair` as field list items
* Replace `icons` list with `has_icons` flag, thus fixing memleak
* Replace `purple_request_field_list_get_icons` with `purple_request_field_list_has_icons`
Testing Done:
Compile and run.
Reviewed at https://reviews.imfreedom.org/r/563/
# UPDATING VERSION NUMBERS FOR RELEASES
#
# The version number is:
# <major>.<minor>.<micro><extra>
#
# micro += 1
#
# If any functions have been added to libpurple, Pidgin, or Finch:
# micro = 0
# minor += 1
#
# If backwards compatibility has been broken in libpurple, Pidgin, or Finch:
# micro = 0
# minor = 0
# major += 1
# purple_soversion += 1
#
# extra should be similar to one of the following: