fix Code highlighting don't work properly or don't detect the language
- remove legacy code highlighter library (hljs.js), hljs.js origin project is dropped.
- add new code highlighter library (highlighter.js - http://highlightjs.org/)
Now, If one or both of the files are too big to show or get the
difference from them, Yobi show an error message different from
one for the case if the difference is oversized.
This also fixes an error have occured when render small diff of an
oversized file because FileDiff.getError returns A_SIZE_EXCEEDED or
B_SIZE_EXCEEDED if the file is larger than the FileDiff.LINE_LIMIT. If
the diff is not larger than the limit, it should be able to rendered
even if the file is larger than the limit but small enough not to raise
And add tests for some exceptional cases.
Before referring original issue properties for the first time, to call update() of modifieid issue brings about the issue because of lazy loading.
The codes that load original issue properties are moved above calling update() of modified issue.