grim/pidgin

Remove the GtkAlignment from PidginCredentialsPage as it's deprecated.

Testing Done:
Compiled and ran locally. Note that glade 3.38 doesn't show the margin on load, but if you tweak the value you'll see that it does work.

Reviewed at https://reviews.imfreedom.org/r/484/
if ENABLE_DOC
subdir('reference')
endif
if ENABLE_GTK
pidgin_man = configure_file(
input : 'pidgin3.1.in',
output : 'pidgin3.1',
configuration : man_conf,
install : true,
install_dir : get_option('mandir') / 'man1')
endif
if enable_consoleui
finch_man = configure_file(
input : 'finch3.1.in',
output : 'finch3.1',
configuration : man_conf,
install : true,
install_dir : get_option('mandir') / 'man1')
endif