added in a 404 image, error handler code and used the corresponding function for thimble's 404 page

fixed the white spacing issues and seprated methods for error handling and nunjucks into their own files

fixed the white spacing issues and seprated methods for error handling and nunjucks into their own files removing the commented out nunjucks code

forgot a new line in the nunjucks file

made errorMessage result in friendly error mesage text

changed white spacing
Merge pull request #257 from elnushaj/bug884351

fixed bug 884351, create a custom 404 page for thimble
NOBUG - Update messages.json
add tutorial pane

add localization for tutorial

add tutorial smartlines

tutorial fixes and refactoring

locale strings for tutorial button titles

tutorial second round edits

remove trailing whitespace
slowparse update
Merge pull request #259 from Pomax/bug911169

in the mixed content world, we are now all winners!
0.1.20
Merge pull request #256 from thomaspark/bug920723

Bug 920723 - Implement new tutorial functionality
0.1.21
[hotfix] anchors do not count towards mixed content

see https://bugzilla.mozilla.org/show_bug.cgi?id=928753
0.1.22