Pagination with "View All" option

Hi All,

I’m struggling trying to add a new link to pagination to show all posts on one page, ie. to remove pagination.

Ultimately I’m trying to achieve this <prev 1 2 3 next> view all>

I’m using the pagination code below:

[code moderated per forum rules - please use the pastebin]

This code works great but I don't know how to edit it to add a view all button, I've gathered that I'll likely need to use add_query_var() and get_query_var(), but not sure how or where to use them. Any help would be really appreciated.