Remove whitespace as well when removing a node

[RheingoldRiver]

Currently, when using code.remove(node), some whitespace (specifically new lines) is left behind, which can lead to display errors on the page in addition to extra whitespace on the source for editors to deal with.

Related: #268, #55, #265, #266

I think how it should behave (and how I've implemented it in my own tools with a workaround, see #268) is:

In the case of:

text here

{{MyTemplate}}

text here

aka, \n\n{{MyTemplate}}\n\n, after MyTemplate is removed, only \n\n should be left behind;

in the case of:

text here
{{MyTemplate}}
text here

aka, \n{{MyTemplate}}\n, after MyTemplate is removed, only one \n should be left behind;

finally, at the beginning of a document,

{{MyTemplate}}
text here

The \n should be removed;

and otherwise no whitespace is stripped.

[lahwaacz]

I have this already implemented: https://github.com/lahwaacz/wiki-scripts/blob/e459de07f303e87c28ef224c70d6bb02274cc9ca/ws/parser_helpers/wikicode.py#L60-L116

Relevant tests: https://github.com/lahwaacz/wiki-scripts/blob/e459de07f303e87c28ef224c70d6bb02274cc9ca/tests/parser_helpers/test_wikicode.py#L53-L176