add ignore element option

[Yuyz0112]

If some elements were in the ignore list, stop observe and record its value.
We also need a default to ignore list, including some elements like password input and so on.

[Yuyz0112]

1. Form element

• password type input should not be recorded
• customize ignore form element should not be recorded

2. DOM

• customize ignore element and its children nodes should not be recorded

We may have two approaches to customize ignore element.

One is to ignore certain class name/data attribute, such as .rr-ignore, and users could add this class name to the element they do not want to record.

Another one is to add an ignore class name option like ['.a', '#b', '[data-c="true"]'], which was already used in users' apps.

The first one needs users to update their source code when the second one may cause extra complexity and potential performance issue.

Personally, I tend to implement the first one because most apps do not already have some markups for privacy usage. And if we provided the second solution, users may define a class name like .ignore which also need to update the source code.

Any feedback is welcomed.

[Yuyz0112]

1. An element with the class name .rr-block will not be recorded. Instead, it will replay as a placeholder with the same dimension.
2. An element with the class name .rr-ignore will not record the input events.
3. input[type="password"] will be ignored as default.