feature(loading): added mode to loading directive + service.

[emoralesb05]

Description

Added mode to loading component so it can be created with either LoadingMode.Determinate or LoadingMode.Indeterminate.
#80

What's included?

• Added enum for LoadingMode.Determinate and LoadingMode.Indeterminate.
• Added loadingMode input to TdLoadingDirective which accepts either LoadingMode or 'determinate'|'indeterminate'.
• Added setValue(name: string, value: number): boolean method to TdLoadingService which is only successful if loading is set to LoadingMode.Determinate or 'determinate'.
• Added reset flag in TdLoadingComponent so its refreshed before removing it from DOM. (else the animation going from the previous value to 0 would happen when the component is reattached again)
• Kept protractor hack intact so it does not timeout when loading mask is used on 'indeterminate' mode. (md-progress-circle setInterval() usage affects protractor since it does not let it sync)
• Updated docs/demos with mode usage.

Test Steps

• ng serve
• Go to http://localhost:4200/#/components/loading
• Play with demo and see how it works
• ⌚

Screenshots or link to CodePen/Plunker/JSfiddle