Add a setting to allow the current buffer in `helm-source-projectile-buffers-list`

[marshall-lee]

Expected behavior

helm-source-projectile-buffers-list should either return or filter out the current buffer from the candidates list depending on a setting.

Actual behavior

helm-source-projectile-buffers-list always filters out the current buffer.

Proposal

Inspired by the similar setting for Ivy called counsel-projectile-remove-current-buffer https://github.com/ericdanan/counsel-projectile/blob/40d1e1d4bb70acb00fddd6f4df9778bf2c52734b/counsel-projectile.el#L521-L526 I propose to add a similar setting called helm-projectile-remove-current-buffer to allow the customization of how helm-source-projectile-buffers-list behaves.

~~One common example of why it's useful is when you set projectile-switch-project-action to helm-projectile which shows the list of buffers. I switch between projects quite often and it's always a pain that I cannot select a most recent buffer quickly because it's skipped from the buffers list.~~ This is actually fixed by #178