Implement component discovery mechanism and make components self registrable

List of changes

1. Provide simple component.info files (in plain text or XML form) for all the components
Example file's contents (for plain text version) would be:
name = CiviContribute
namespace = CRM_Contribute
Initial thinking - XML would be better, since we use it in different places already and doesn't force us to implement mechanism for parsing yet another type of files.

2. Implement a mechanism to go through the $civicrm_root recursively and discover all the .info files.

3. Implement civicrm_components table and discovered .info files intelligent merging.