Make the load API consistent

[Danielku15]

Description

Currently there are multiple ways to load tracks or scores into alphaTab to be ultimately rendered. This API is not consistent and 100% clear to users. e.g. the load method accepts a URL that will download a file, and then use some previously configured track indexes for display. The renderTracks method acceps a score, track indexes and a bool for rendering.

Possible Solutions

One or max 2 dedicated methods should exist that allow full flexibility of passing in to alphaTab what to load and display.

[Danielku15]

The new API consist now of following methods:

• Render() which simply rerenders the current configuration
• RenderScore(Score score, int[] trackIndexes = null) to render the tracks of an already available score.
• RenderTracks(Track[] tracks) to render an already available track list
• Load(object data, int[] trackIndexes = null) to decode/load the score from the given data object and render it.