Completely redo how mxisd configuration gets generated

This change is provoked by a few different things:

- #54 (Github Pull Request), which rightfully says that we need a
way to support ALL mxisd configuration options easily

- the upcoming mxisd 1.3.0 release, which drops support for
property-style configuration (dot-notation), forcing us to
redo the way we generate the configuration file

With this, mxisd is much more easily configurable now
and much more easily maintaneable by us in the future
(no need to introduce additional playbook variables and logic).

CHANGELOG.md

@@ -1,3 +1,43 @@
+# 2019-01-11
+
+## (BC Break) mxisd configuration changes
+
+To be more flexible and to support the upcoming [mxisd](https://github.com/kamax-io/mxisd) 1.3.0 (when it gets released),
+we've had to redo how mxisd gets configured.
+
+The following variables are no longer supported by this playbook:
+
+- `matrix_mxisd_ldap_enabled`
+- `matrix_mxisd_ldap_connection_host`
+- `matrix_mxisd_ldap_connection_tls`
+- `matrix_mxisd_ldap_connection_port`
+- `matrix_mxisd_ldap_connection_baseDn`
+- `matrix_mxisd_ldap_connection_baseDns`
+- `matrix_mxisd_ldap_connection_bindDn`
+- `matrix_mxisd_ldap_connection_bindDn`
+- `matrix_mxisd_ldap_connection_bindPassword`
+- `matrix_mxisd_ldap_filter`
+- `matrix_mxisd_ldap_attribute_uid_type`
+- `matrix_mxisd_ldap_attribute_uid_value`
+- `matrix_mxisd_ldap_connection_bindPassword`
+- `matrix_mxisd_ldap_attribute_name`
+- `matrix_mxisd_ldap_attribute_threepid_email`
+- `matrix_mxisd_ldap_attribute_threepid_msisdn`
+- `matrix_mxisd_ldap_identity_filter`
+- `matrix_mxisd_ldap_identity_medium`
+- `matrix_mxisd_ldap_auth_filter`
+- `matrix_mxisd_ldap_directory_filter`
+- `matrix_mxisd_template_config`
+
+You are encouraged to use the `matrix_mxisd_configuration_extension_yaml` variable to define your own mxisd configuration additions and overrides.
+Refer to the [default variables file](roles/matrix-server/defaults/main.yml) for more information.
+
+This new way of configuring mxisd is beneficial because:
+
+- it lets us support all mxisd configuration options, as the playbook simply forwards them to mxisd without needing to care or understand them
+- it lets you upgrade to newer mxisd versions and make use of their features, without us having to add support for them explicitly
+
+
 # 2019-01-08
 
 ## (BC Break) Cronjob schedule no longer configurable