Add Custom Content Block to /investments in multi heading budget

[coslajohn]

User Story

At the moment it is possible to add custom content blocks to pages for individual headings in a budget. If there is only one heading then this will place the custom content block on the /investments page as in this screenshot

In a multi heading budget it is possible to add custom content to each heading

However there is no way way to add custom content to /investments in a multi heading budget

Why is this Needed?

When voting in a multi heading budget there is no easy way to navigate from /investments which is the list of all investments to the investments in a specific district/heading.

When voting, we have found it helpful to use an action button to direct users to vote at /investments to reduce the number of clicks to vote

In a mutli heading vote when you can only vote in one heading we can't use this short cut. If a user lands at /investments they see all proposals for all headings

There are three possible complementary solutions

1. add links to all headings/districts to the /investments page
2. allow custom content blocks to be added to /investments
3. Add a Headings filter next to Highest Rated and Random