Migrate to Bootstrap 4

[adamkudrna]

Steps:

• Rewrite LESS source code to SCSS
• Modify/fork/replace third party components: select2, datetimepicker
• Work in long-term branch in parallel with stable (Bootstrap 3) version

Risks:

• Work with third party components (datetimepicker, select2) can get out of control

[adamkudrna]

Not actionable until version 4 is released.

[saraedum]

Bootstrap 4 has been released. Are the any plans on migrating to bootstrap 4 now? (Btw., it's a bit confusing that you reference this closed issue in your README.md.)

[adamkudrna]

@saraedum Thank you for pointing this out. Yes, we are planning to begin the migration in upcoming months.