feat: Calendar Events implemented.

[develoopeer]

• Ics files widely used format to represent calendar info parsed via https://github.com/arran4/golang-ical library. It is super lightweight and can parse ics files from different sources. Google calendar, Trello and local files were tested by me.

• Events in calendar will be highlighted with color-primary color, and have hover text.

• If you have more than 1 event at the same day for one day, only first one will be displayed. Complete version looks like this:

• Icsurl option added to yaml configuration

• type: calendar icsurl: https://testsite/validurl.ics

  
  For example to grab url from google calendar you need to make your calendar public, click on calendar settings and get url from ics field. [Instruction](https://support.pushpay.com/s/article/How-do-I-get-an-iCal-feed-from-Google-Calendar). Same goes for [Trello](https://support.atlassian.com/trello/docs/using-the-calendar-power-up/)

• Events will be updated every hour, because of default Calendar Widget Initialize function declared with withCacheOnTheHour() function. This time can be increased or decreased, but i don`t think it is necessary.

• I feel like icsurl option can be replaced with icsurls option, to allow you gather events from different sources. This behavior can be simply implemented, but i don`t know is it really useful. I need your opinion for that.

[develoopeer]

Hello @svilenmarkov. Will this PR be merged in the near future?

[svilenmarkov]

@develoopeer Hey, yeah sorry, calendar events were planned for v0.7.0 so I'll get it merged before that comes out, just wanted to make a couple of changes that I haven't had the chance to work on yet.

[develoopeer]

Ooh i got it. I will resolve emerging conflicts in this PR in near future. Hope v0.7.0 will be coming out soon.