Remove outdated tasks

[DavertMik]

Most of those tasks were introduced to build frontend assets, however, they are not used in a modern world. We can safely remove them in next major version

• Gulp
• Bower
• Assets

[ivangretsky]

I do not think that those (maybe except for Bower) should be removed altogether, A lot of projects still use those. Maybe move them to 1st party plugins instead and create a plugin page on the website?