pidgin/pidgin

Add a description to PurpleCredentialProvider and show it in the preferences selector

Testing Done:
Compiled and ran locally.

Reviewed at https://reviews.imfreedom.org/r/539/
if PLUGINS
subdir('kwallet')
if nettle.found()
internalkeyring_plugin = library('internalkeyring', 'internalkeyring.c',
dependencies : [nettle, libpurple_dep],
name_prefix : '',
install : true, install_dir : PURPLE_PLUGINDIR)
endif
if secretservice.found()
secretsservice_plugin = library('secretservice', 'secretservice.c',
dependencies : [secretservice, libpurple_dep],
name_prefix : '',
install : true, install_dir : PURPLE_PLUGINDIR)
endif
if IS_WIN32
wincred_plugin = library('wincred', 'wincred.c',
dependencies : [libpurple_dep],
name_prefix : '',
install : true, install_dir : PURPLE_PLUGINDIR)
endif
endif # PLUGINS