remove fetchAllDocuments method

[benoitvidis]

This PR removes the fetchAllDocuments method from the SDK, which can be better replaced by a search + fetchNext call (documentation to come).

[samniisan]

ok for me after checking the Travis error in offlineQueue.test.js

[codecov-io]

Codecov Report

Merging #228 into 5.x will increase coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              5.x     #228      +/-   ##
==========================================
+ Coverage   98.24%   98.51%   +0.27%     
==========================================
  Files          17       17              
  Lines        2050     2027      -23     
  Branches      590      583       -7     
==========================================
- Hits         2014     1997      -17     
+ Misses         36       30       -6

Impacted Files	Coverage Δ
src/Collection.js	98.64% <ø> (+1.78%)	⬆️

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