Provide more dynamic frequencies

Problem/Motivation

Currently, I need to add more frequencies for the view mode switch to match with my desired result.
In my case, I have a listing page of X items with 3 columns and I must first make the change after the 6th items and then after the 4th items.

Here is the desired rendering:

[AVM][][]
[][][AVM]
[][][]
[AVM][][]
[][][AVM]
[][][]
...

* AVM: Alternative View Mode

I have read the last features that allows you to configure the view mode switch line by line. However, I need to have a dynamic rendering and not limit it to X items. I also think that the proposed is more cleaner for my case.

Proposed resolution

Allow the ability to add more frequencies dynamically by using a check box item. The patch allows adding 2 additional frequencies.

User interface changes

Thx for your very useful module.