CSS / Canvas Filters for Working Transcription Image

_From @cubap on October 16, 2015 5:38_

Apply some basic CSS filters and possibly allow for more advanced canvas pixel manipulations:
### CSS
1. Brightness
2. Contrast
3. Invert
4. Saturation / Grayscale
### Canvas Element
1. Edge detection
2. Custom convolution/Sobel filters

Note: I expect that the case for this is clarifying text, but others and the reason for them would be helpful to add to this ticket (bonus points awarded for image samples).

_Copied from original issue: cubap/TPEN3#3_