fixes a possible "You must call getSegmentRequestForTime first." exception after seeking
fixes DashManifestExtensions.getRegularPeriods for the case where Early Available Periods present in mpd
fixes video element switch for multi period mpds after player reset
Merge pull request #326 from MSOpenTech/development

Bugfixing
adds a reference for a new RequestModifierExtensions class and removes a reference for the removed TokenAuthentication class
Merge pull request #327 from MSOpenTech/development

Adds a reference for a new RequestModifierExtensions class and removes a...
Correct MPDHelper.js name in Gruntfile.js

The wrong name will result in Task "jasmine:tests" failed:
TypeError: 'undefined' is not an object (evaluating 'mpdHelper.getAdaptationWithSegmentTemplate'
Merge pull request #329 from qjia7/MpdHelper

Correct MPDHelper.js name in Gruntfile.js