(#1533) Generify org.cactoos.list package

[DmitryBarskov]

For #1533:

Many thanks for your contribution, we truly appreciate it. We will appreciate it even more, if you make sure that you can say "YES" to each point in this short checklist:

• Description begins with the issue's number, then enumerates the changes - summarized - in bulletpoints
• Description does not contain GitHub keywords (https://help.github.com/articles/closing-issues-using-keywords/).
• You ran the build locally and it passed (see .travis.yml for all checks performed on PRs)

This article will help you understand what we are looking for: http://www.yegor256.com/2015/02/09/serious-code-reviewer.html

Thank you for your contribution!

[codecov-commenter]

Codecov Report

Merging #1634 (b7cbd17) into master (2d3d898) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #1634   +/-   ##
=========================================
  Coverage     90.10%   90.10%           
  Complexity     1603     1603           
=========================================
  Files           298      298           
  Lines          3749     3749           
  Branches        122      122           
=========================================
  Hits           3378     3378           
  Misses          337      337           
  Partials         34       34           

Impacted Files	Coverage Δ
src/main/java/org/cactoos/list/Joined.java	100.00% <ø> (ø)
src/main/java/org/cactoos/list/Immutable.java	100.00% <100.00%> (ø)
...n/java/org/cactoos/list/ImmutableListIterator.java	91.66% <100.00%> (ø)
...main/java/org/cactoos/list/JoinedListIterator.java	75.60% <100.00%> (ø)

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