Add prepend/append options to BaseListView

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌

[codecov]

Codecov Report

Attention: Patch coverage is 16.66667% with 10 lines in your changes missing coverage. Please review.

Project coverage is 85.90%. Comparing base (64814af) to head (972d229).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/BaseListView.php	16.66%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #273      +/-   ##
============================================
- Coverage     86.29%   85.90%   -0.39%     
- Complexity      632      636       +4     
============================================
  Files            50       50              
  Lines          2152     2164      +12     
============================================
+ Hits           1857     1859       +2     
- Misses          295      305      +10     

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[samdark]

What is the use case? Why not use the template itself?

prepended
<?= GridView::widget() ?>
appended

[vjik]

prepended
<?= GridView::widget() ?>
appended

prepend/append added blocks into container:

<container>
prepend
... body ...
append
</container>

This is convient for configuration. For example, add overlay block that visualizes loading process.