"gitblit keys ls" now defaults to showing an indexed list of fingerprints which almost matches the output of "sshadd -l".  The indexes are useful specifying key(s) to remove using "gitblit keys rm <index>".  This is an important improvement for key management.

Fix commented out code. Now failure is reported as:

  Internal server error (user admin) during gitblit version

Managers are mostly declared in dependency order.  Managers with fewer dependencies are first.  They are likely to be components of other managers. Also eliminated import artifacts from the cherry-pick.

Example plugin is provided [1].

[1] https://github.com/davido/gitblit-cookbook-plugin

Plugins are stored in `${baseFolder}/plugins` and are loaded
during startup by the PluginManager.

A plugin defines it's metadata in META-INF/MANIFEST.MF:

    Plugin-Class: com.gitblit.plugins.cookbook.CookbookPlugin
    Plugin-Dependencies: foo, bar
    Plugin-Id: gitblit-plugin
    Plugin-Provider: John Doe
    Plugin-Version: 1.0

Plugins can define extension points that can be implemented
by other plugins and they can depend on other plugins:

    Plugin-Dependencies: foo, bar

During the load phase, a directed acyclic graph is built and the loading
order of the dependency chain is reversed using a topological sort;
parent followed by children. The parent plugin classloader is the
combined classloader of all parent plugins.

Change-Id: I738821fa2bff02a5dbe339a944cc7e3c4dd8e299

Conflicts:
	src/main/java/com/gitblit/transport/ssh/SshDaemon.java