add REST documentation for config module

Apparently not, but if that's the case, perhaps we shouldn't define the endpoint. Here's the trace:

Define the endpoint for admin tenant with no tenant alias specified:

    OAE.globalAdminRouter.on('post', '/api/config/clear', _handleClearConfig);

In `_handleClearConfig` try to determine the tenant:

    var _handleClearConfig = function(req, res) {
        var tenantAlias = req.params.tenantAlias || req.ctx.tenant().alias;
        ConfigAPI.clearConfig(req.ctx, tenantAlias, configFields, function(err) {

In the API, return an error if no tenant is specified:

     var clearConfig = module.exports.clearConfig = function(ctx, tenantAlias, configFields, callback) {
        validator.check(tenantAlias, {'code': 400, 'msg': 'Missing tenant alias'}).notEmpty();

Should I delete the code that's defining the endpoint for the admin router?