Code formatting: Change indentation style to space

[olofhagsand]

In clixon source, there is an .editorconfig as follows

indent_style = tab
indent_size  = 4

Currently there are TABS inserted in places that are not completely logical.
It is proposed to remove the use of TABS completely, ie always use spaces instead of TABs in C-code.
In emacs, this means: (setq-default indent-tabs-mode nil)
A small sample of other C-based projects seems to indicate that this seems common practice.
It is therefore also proposed to update editorconfig to (at least):

indent_style = space
indent_size  = 4

This will result in a major code change (ie only appearance), replacing all tabs to spaces.
See also
#373

[olofhagsand]

All cligen and clixon code changed from TAB formatting to SPACE.