feat: support weekly/monthly view in barchart visualization

[ErikBjare]

This is pretty great.

Started off trying to implement a 'trends' view (as described in #289), but found it a lot easier to start with just adding week/month support to the barchart.

[codecov]

Codecov Report

Merging #292 (ce117f2) into master (4d8e5ee) will decrease coverage by 0.15%.
The diff coverage is 9.24%.

@@            Coverage Diff             @@
##           master     #292      +/-   ##
==========================================
- Coverage   15.91%   15.76%   -0.16%     
==========================================
  Files          22       24       +2     
  Lines        1062     1142      +80     
  Branches      110      127      +17     
==========================================
+ Hits          169      180      +11     
- Misses        848      912      +64     
- Partials       45       50       +5     

Impacted Files	Coverage Δ
src/route.js	0.00% <0.00%> (ø)
src/util/datasets.js	0.00% <0.00%> (ø)
src/util/filters.js	0.00% <0.00%> (ø)
src/store/modules/activity.ts	6.69% <3.03%> (+0.59%)	⬆️
src/util/timeperiod.ts	18.18% <18.18%> (ø)

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[lgtm-com]

This pull request introduces 2 alerts when merging 898883b into 4d8e5ee - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 2 alerts when merging ce117f2 into 4d8e5ee - view on LGTM.com

fixed alerts:

• 1 for Unused variable, import, function or class
• 1 for Template syntax in string literal