Add an option to check for updates forcibly

[ameshkov]

Currently, we cache the version.json contents for 8 hours. There should be a way to reload the file contents forcibly.

Here's how to do it in the UI:

1. Add a "Refresh icon" next to the version: https://uploads.adguard.com/up04_r0rdb_AdGuard_Home.png (also change "version" to "Version")
2. Click on this icon should trigger the update check.
3. If a new version is found, show the regular "new version found" topline.
4. If nothing found, show notification: "AdGuard Home is up-to-date.

[ghost]

Let's do some enhancement

• ☐ Check program updates automatically (enabled by default)
  (or ☐ Check for program updates every 8 hours/days)
  [already adguardhome v0.96 check updates and notify user]
  note: necessary 'Check Update' or above mentioned 'Refresh' button too.

• ☐ Automatically download program updates
  (if checked, program updates will be automatically downloaded. You will still need to choose when to install them)

• ☐ Automatically install program updates
  (or ☐ Automatically install program updates in critical situations)

If user disabled that all then AdGuardHome shouldn't make any request and Third option fulfill # 813 feature request.

[Eyeborgs]

@Archivebase
This is what I want

But it is still desirable that I control the silent update as well, that is, the third option.
Sorry, I'm just really worried about this because I love total control.