feat(tabbar): add activeIcon property

[cipchk]

• close weui-tab组件是否可提供两个property：选中时候显示的图标和未选中时候显示的图标 #135

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/cipchk/ngx-weui/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #139 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
+ Coverage    86.1%   86.13%   +0.02%     
==========================================
  Files         102      102              
  Lines        1914     1918       +4     
  Branches      263      264       +1     
==========================================
+ Hits         1648     1652       +4     
  Misses        140      140              
  Partials      126      126

Impacted Files	Coverage Δ
components/tab/tabbar.component.ts	100% <ø> (ø)	⬆️
components/tab/tab.directive.ts	100% <100%> (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 ba9ccd7...818b9c3. Read the comment docs.

[codecov]

Codecov Report

Merging #139 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
+ Coverage    86.1%   86.13%   +0.02%     
==========================================
  Files         102      102              
  Lines        1914     1918       +4     
  Branches      263      264       +1     
==========================================
+ Hits         1648     1652       +4     
  Misses        140      140              
  Partials      126      126

Impacted Files	Coverage Δ
components/tab/tabbar.component.ts	100% <ø> (ø)	⬆️
components/tab/tab.directive.ts	100% <100%> (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 ba9ccd7...818b9c3. Read the comment docs.