Popover and Tooltip arrows are off-center vertically and horizontally

[mcoker]

I see this has been addressed in #2855 and #3940 but it still appears to be an issue.

Using a left/right position for the popover and tooltip, in bootstrap 4, the popover arrow height is 16px and tooltip arrow height is 12px.

The negative margin to center the popover arrow is -8px

https://github.com/valor-software/ngx-bootstrap/blob/development/src/popover/popover-container.component.ts#L18-L25

The negative margin to center to tooltip is -6px

https://github.com/valor-software/ngx-bootstrap/blob/development/src/tooltip/tooltip-container.component.ts#L25-L32

This works fine in bootstrap 4, but in bootstrap 3, the popover height is 22px and the tooltip is 10px, so the negative margins to center those elements should be -11px and -5px, respectively.

Bug description or feature request:

Plunker/StackBlitz that reproduces the issue:

You can see this on

https://valor-software.com/ngx-bootstrap/#/popover

https://valor-software.com/ngx-bootstrap/#/tooltip

Versions of ngx-bootstrap, Angular, and Bootstrap:

ngx-bootstrap: 3.1.2

Angular: n/a

Bootstrap: 4.0.0