Added the infrastructure necessary for plug-ins to be able to add their own...

Added the infrastructure necessary for plug-ins to be able to add their own settings instead of having settings added to existing ones. In particular "target.disable-kext-loading" was added to "target" where it should actually be specific to the the dynamic loader plugin. Now the plug-in manager has the ability to create settings at the root level starting with "plugin". Each plug-in type can add new sub dictionaries, and then each plug-in can register a setting dictionary under its own short name. For example the DynamicLoaderDarwinKernel plug-in now registers a setting dictionary at:

plugin
    dynamic-loader
        macosx-kernel
            (bool) disable-kext-loading
            
To settings can be set using:

(lldb) settings set plugin.dynamic-loader.macosx-kernel.disable-kext-loading true

I currently only hooked up the DynamicLoader plug-ins, but the code is very easy to duplicate when and if we need settings for other plug-ins.

llvm-svn: 166294