Limit number of pipelineruns and taskruns in a tree

[evidolob]

This PR add limit on number of tree item for pipelineruns and taskruns, by default limit is 5 but can be changed in a preferences(treePaginationLimit option)

Also this PR changes the way how pipelineruns and taskruns are sorted and listed in a tree.
Now all of them sorted by creation time and newest showing first.

Demo:

Fix for: #79

[codecov-io]

Codecov Report

Merging #127 into master will decrease coverage by 0.13%.
The diff coverage is 74.41%.

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
- Coverage    74.4%   74.26%   -0.14%     
==========================================
  Files          19       19              
  Lines        1090     1127      +37     
  Branches      157      164       +7     
==========================================
+ Hits          811      837      +26     
- Misses        279      290      +11

Impacted Files	Coverage Δ
src/extension.ts	86.74% <100%> (+0.49%)	⬆️
src/tkn.ts	77.8% <72.5%> (-0.95%)	⬇️

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[siamaksade]

/lgtm