feat(filters): add updateSingleFilter for a single external filter

[ghiscoding]

No description provided.

[codecov]

Codecov Report

Merging #699 (91a95ba) into master (b8d1d14) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #699   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          159       159           
  Lines        10571     10590   +19     
  Branches      3716      3727   +11     
=========================================
+ Hits         10571     10590   +19     

Impacted Files	Coverage Δ
...dules/angular-slickgrid/services/filter.service.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b8d1d14...91a95ba. Read the comment docs.