app.middleware: verify serial exec of handlers

Add a test verifying that middleware handlers are executed serially.
server-app: middleware API improvements

 - Rename `config.config` to `config.params`
 - Modify methods to return `this` (fluent API)
server-app: improve jsdoc comments
AccessToken: optional `options` in findForRequest

Fix `AccessToken.findForRequest` to correctly handle the case when
the options argument was omitted:

    AccessToken.findForRequest(req, cb);
Merge pull request #792 from strongloop/feature/allow-serial-phase

app.middleware: verify serial exec of handlers
Minor: update jsdoc for PersistedModel.updateAll
Fixing the model attach
Fix the model name for hasMany/through relation
Update CONTRIBUTING.md
Merge pull request #826 from BuddyHOPP/master

Update CONTRIBUTING.md
Merge pull request #819 from BuddyHOPP/fix/jsdoc_update

Minor: update jsdoc for PersistedModel.updateAll
Merge pull request #796 from strongloop/feature/cleanup-middleware-config-opts

Cleanup middleware config opts
Merge pull request #814 from strongloop/feature/fix-issue-811

Fix the model name for hasMany/through relation
Merge pull request #822 from wfgomes/patch-2

Fixing the model attach
Scope app middleware to a list of paths

Add a new argument to `app.middleware` allowing developers
to restrict the middleware to a list of paths or regular expresions.

Modify `app.middlewareFromConfig` to pass `config.paths` as the second
arg of `app.middleware`.

Examples:

    // A string path (interpreted via path-to-regexp)
    app.middleware('auth', '/admin', ldapAuth);

    // A regular expression
    app.middleware('initial', /^\/~(admin|root)/, rejectWith404);

    // A list of scopes
    app.middleware('routes', ['/api', /^\/assets/.*\.json$/], foo);

    // From config
    app.middlewareFromConfig(
      handlerFactory,
      {
        phase: 'initial',
        paths: ['/scope', /^\/(a|b)/]
      });
Merge pull request #813 from strongloop/fix/AccessToken.findForRequest

AccessToken: optional `options` in findForRequest
Merge pull request #837 from strongloop/feature/scope-middleware-to-path

#794 - Scope app middleware to a list of paths
Expose more loopback middleware for require
Merge pull request #834 from strongloop/feature/expose-loopback-middleware

Expose more loopback middleware for require
v2.8.0