Multiple Overriding Configuration Files Support with Default Configuration Paths as Convention

In summary, we can improve the following and we can have some conventions:

(1) Let's allow overriding by 'CompositeConfiguration', which reduces copying-all-properties.
For example, system administrators do not need to copy all of /WEB-INF/hst-config.properties into file://${catalina.base}/conf/hst.properties.
They can just add a few properties only that they want to override.

(2) Let's have the following convention as ordered by priority when reading a property:
a) system properties (optional if exists. e.g., '-Dprop1=value1'). See an example below.*
b) properties file as defined by context init parameters, hst-configuration.xml and hst-config-properties (optional if exists; backward compatible)
c) file://${catalina.base}/conf/hst.properties (optional if exists; so system administrators won't need to define the context init parameter described in 2-b explicitly any more.)
d) /WEB-INF/hst-configuration.xml (optional if exists) otherwise /WEB-INF/hst-config.properties (optional if exists)

• With this option, I meant the following scenario.
  Let's suppose we have file://${catalina.base}/conf/hst.properties with only one line to override something as follows:

solr.url = http://www.example.com/solr

I'd like to add one more possibility to allow system administrator to change this in the command line, too:
For example,

$ export CATALINA_OPTS="-Dsolr.url=http://solr.example.com"
$ ./catalina.sh start