Editor-related: mark spinejson files as textual

Merge pull request #136 from defold/DEFEDIT-7586

Mark spinejson resource type as textual

Better error messages

Better error message when:

• a bone cannot be found using "spine.get_go()";
• IK constraint target cannot be found using "spine.set_ik_target_position()".

Improved performance of vertex generation

• The vertex data memory is allocated once, as opposed to many times for each spine slot.

Rebuilt plugins in headless mode

Rebuilt the content plugin using headless mode.
Solves the issue of needing some dependencies on CI builds.

Spine 4.1

This version of the extension uses Spine 4.1 which means all the Spine models in the project should be updated to be able to use this plugin.

This version supports Sequences (Frame-by-frame animations)

Expose "playback rate" and "offset" to spine component

Now it's possible to set up initial "playback rate" and "offset" in the spine component itself:

Internal texture format update

Supports Defold 1.4.4+

In this release we've make a compile fix to support a change in our internal representation of a texture.

Fix crash in CompSpineModelSetProperty

See details in #79

Defold 1.4.2

There were some editor data model changes to improve the performance of projects with Spine content. If you are using 1.4.2, you should update your Spine dependency to this version.

User-facing changes:

• Editor: Apply color to Spine gui objects in scene view.
• Editor: Saving gui files that contain Spine gui objects takes less time.

Added Create GO. Bones checkbox for SpineModel

The new checkbox Create GO Bones (default: false), controls if the Spine model should create game objects for each bone in the model.

Breaking change:
Since this version, the default value is false (it was previously true) in order to save resources by default.

• Migration: Enable the check box to use the old behavior.