Port to GTK3

[rhl-bthr]

i-can-read is dependent on GTK+ 2 API and must be ported to GTK+ 3 API.

(Should anybody take this, please look at my work in progress. Remaining changes are porting drawing code to Cairo drawing code.)

[yell0wfl4sh]

@Pro-Panda status?

[rhl-bthr]

@yashagrawal3
As mentioned above, the port is partially complete. I am not currently working on the same.
You may continue from my work in progress

[yell0wfl4sh]

@Pro-Panda OK! thanks.

[yell0wfl4sh]

WIP https://github.com/yashagrawal3/i-can-read-activity/tree/gtk3
Continued work from Pro-Panda's fork. page.py needs a lot of work, port to cairo left.
Following similar changes as was made in sugarlabs/AEIOU@4f7fad4
@quozl suggestions are welcomed.

[quozl]

Reviewed, thanks. I wasn't sure what was happening. I suggest using smaller commits, and more of them, with brief description of why you changed something.

[yell0wfl4sh]

@quozl @chimosky spent another complete day on it, tried to port every line from start ended up getting the same error. I have tried by all means to solve this, I need some help on this issue.
See my new branch: https://github.com/yashagrawal3/i-can-read-activity/tree/gtk3port

[quozl]

need some help on this issue.

Looks like you since fixed your problem with unexpected unicode strings in the generated SVG XML stream. However, some more work seems to be needed.

Adding missing link between pull request and issue; #8