Fixed issue with bold in issuable sidebar
## What does this MR do?
~~The sidebar contained both normal font weight & bold font weight, so this standardises them to bold.~~
After looking at the designs, i've updated the font weights & colors throughout the sidebar to correctly match them
## Screenshots (if relevant)

See merge request !4398
Manually create todo for issuable
## What does this MR do?
Adds a button to the sidebar in issues & merge requests to allow users to manually create a todo item themselves.
## What are the relevant issue numbers?
Closes#15045
## Screenshots (if relevant)



See merge request !4502
Fixed issue where label filtering didnt work
## What does this MR do?
The filterable option was missing which meant labels in the dropdown couldn't be filtered. This fixes that.
## What are the relevant issue numbers?
Closes#18375
See merge request !4556
Add milestone expire date to the right sidebar
## What does this MR do?
Shows milestone expire date tooltip in the sidebar. It also shows the tooltip when sidebar is collapsed.
## Are there points in the code the reviewer needs to double check?
`common_utils.js.coffee` and `milestones_helper.rb` should be reviewed deeply.
## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/17355
## Screencast

See merge request !4448
This will be useful when you want to ask for the
number of items and later iterate over them, without
needing to ask if the association is load or not.
So you avoid extra database queries
Loads move issue dropdown async
To keep the style of the dropdown the same as the other dropdowns in the issue form, it uses select2 rather than our new dropdowns.

Closes#16563
See merge request !4160
Issuable filtering improvements
This improves the filtering of issues and merge requests by creating a single file that encapsulates all the filtering. Previously this was done with a file for issues and a file for merge requests.
Created the ability for the text search to be done alongside other filterables. Previously because this was outside the filterable form, this wasn't possible and would instead do either filter dropdown or text filter - not both. Fixes#4252
Fixed issue with not being able to filter and sort issues without refreshing the page. Fixes#15269
See merge request !3699
Issuable form due date
For some reason, this was never in the original merge request for due date?

Closes#15516
See merge request !3895
This improves the filtering of issues and merge requests by creating a single file that encapsulates all the filtering. Previously this was done with a file for issues and a file for merge requests.
Created the ability for the text search to be done alongside other filterables. Previously because this was outside the filterable form, this wasn't possible and would instead do either filter dropdown or text filter - not both.
Add new shortcuts
Closes#14904
- On a project: `i` To navigate to New Issue page.
- On a issuable: `l` To open Label dropdown on a issuable.
- Global: Typing `?` multiple times now toggles the modal.
See merge request !3686