Implement the password policy UI and finish IPA policy UI

This includes a default password policy
Custom fields are now read from LDAP. The format is a list of
  dicts with keys: label, field, required.
The LDAP-based configuration now specifies:
    ipaUserSearchFields: uid,givenName,sn,telephoneNumber,ou,title
    ipaGroupSearchFields: cn,description
    ipaSearchTimeLimit: 2
    ipaSearchRecordsLimit: 0
    ipaCustomFields:
    ipaHomesRootDir: /home
    ipaDefaultLoginShell: /bin/sh
    ipaDefaultPrimaryGroup: ipausers
    ipaMaxUsernameLength: 8
    ipaPwdExpAdvNotify: 4
This could use some optimization.

ipa-python/ipaerror.py

@@ -123,6 +123,11 @@ LDAP_EMPTY_MODLIST = gen_error_code(
         0x0006,
         "No modifications to be performed")
 
+LDAP_NO_CONFIG = gen_error_code(
+        LDAP_CATEGORY,
+        0x0007,
+        "IPA configuration not found")
+
 #
 # Input errors  (sample - replace me)
 #