New Feature: Conditional Toggling of Setting Fields

Hi, 

This is my recent addition for OptionTree. This feature hides/shows a certain field based on a specified condition of other fields.

Conditions can be specified by specifying the conditions on the UI builder.

Conditions can be like this:

```field_name:is(value)```

```field_name:isnot(value)```

So a particular field will be checked against other fields.

For now, the only working field to check against are dropdowns and radio buttons. Checkbox doesn't work yet.

Please do the necessary adjustments and optimizations if you want to implement this.

Thanks!