Tests: cursorNext/cursorPrev

[aqkhan]

Fixes #806

[aqkhan]

@raineorshine I've found the following issues with the action-creators cursorNext and cursorPrev:

• Both the action-creators do not work with the sorted context as expected.
• Both the action-creators do not move the cursor to first child of root when the cursor is not set.

I've fixed the second issue, i.e move the cursor to first child of root when the it is not set but need more time to fix the first issue. I will move forward after your approval.

[raineorshine]

Nicely done!

I did some minor refactors, but otherwise looks great:

• Moved tests to /action-creators/__tests__/ directory.
• Removed unnecessary async/await (it's not obvious that this works since importText appears to be asynchronous and needs to be updated).
• Dispatch multiple actions at once using redux-multi.
• Remove rank from toMatchObject since that creates an unnecessary dependency on importText's somewhat arbitrary ranks.

[raineorshine]

I will merge and you can open another PR for the sort issue! Thanks!