Fixes 2

[MarkE16]

Description

Includes a few fixes and improvements. Several include:

• Ability to edit sliders in the Drawing Toolbar by double-clicking the numerical value displayed next to the slider and typing a value
• Fix eraser tool
• Fix layer previews not drawing the preview on page load
• Ability to persist the canvas position and scaling across browser sessions
• Ability to draw smoother brush strokes using the quadraticCurveTo(...) HTML5 Canvas API

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that causes changes to existing functionality, possibly impacting existing features)

Have you tested your changes?

• I wrote tests for the code I've written.