Customization toolbar and menu

[VolodymyrSh]

Description

What changes are included in this pull request?

Reason

• Bug fix
• [ x ] Feature enhancement
• New feature
• [ x ] Documentation update
• [ x ] Upgrade
• Other

Are you responding to a filed Issue? (bug report, feature request, documentation request, etc)

#2

Testing

Aras Innovator

• Major version: 12.0
• Service pack(s): SP0 | SP1 | SP2 | etc..

Browsers

• [ x ] Internet Explorer 11
• [ x ] Firefox ESR
• [ x ] Chrome
• [ x ] Edge

Does this pull request include known issues?

Add example for custom toolbar or context menu item

Checklist

• [ x ] Did you confirm the Install Steps in the README are still correct?
• [ x ] If this PR adds or changes functionality, did you update the Usage Steps in the README?
• Did you add your GitHub user name to the "Credits" section in the README?