fix and standardize javadoc

[scottinet]

Description

All javadoc errors must be resolved as it is a pre-requisite for bintray publication.

This PR:

• solves javadoc known errors
• fixes erroneous javadoc descriptions
• adds missing javadoc
• applies DRY principle to javadoc by using links instead of repetitions

Other changes

• Remove unused FilterHelper class embryo
• Regroup some overloads separated from their corresponding implementations

[codecov-io]

Codecov Report

Merging #143 into master will increase coverage by 0.37%. The diff coverage is 95.45%.

@@            Coverage Diff             @@
##           master     #143      +/-   ##
==========================================
+ Coverage    91.2%   91.57%   +0.37%     
==========================================
  Files          33       32       -1     
  Lines        4697     4678      -19     
  Branches      437      437              
==========================================
  Hits         4284     4284              
+ Misses        287      268      -19     
  Partials      126      126

Impacted Files	Coverage Δ
...rc/main/java/io/kuzzle/sdk/core/MemoryStorage.java	90.6% <ø> (ø)	:arrow_up:
src/main/java/io/kuzzle/sdk/security/Role.java	100% <ø> (ø)	:arrow_up:
.../io/kuzzle/sdk/responses/NotificationResponse.java	32.25% <ø> (+10.98%)	:arrow_up:
src/main/java/io/kuzzle/sdk/util/QueryObject.java	75% <ø> (ø)	:arrow_up:
src/main/java/io/kuzzle/sdk/core/Room.java	92.03% <ø> (ø)	:arrow_up:
.../kuzzle/sdk/security/AbstractSecurityDocument.java	96.49% <ø> (ø)	:arrow_up:
src/main/java/io/kuzzle/sdk/core/RoomOptions.java	71.42% <ø> (ø)	:arrow_up:
src/main/java/io/kuzzle/sdk/security/User.java	95.95% <ø> (ø)	:arrow_up:
src/main/java/io/kuzzle/sdk/state/KuzzleQueue.java	72.72% <ø> (ø)	:arrow_up:
...ain/java/io/kuzzle/sdk/responses/SearchResult.java	55.55% <ø> (ø)	:arrow_up:
... and 9 more

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