Fix Issues left from mobile design

[jo2]

@romani according to your comment, here is the issue to the remaining minors. I'll take a look at it.

non blocking regressions (can be fixed in separate PRs):
extra line wrapping after small images

extra space (if we try to make rendering awesome, but really ... not a problem):

[jo2]

Second one is an easy fix. source-tag has a 'fix' width of 90%, remove it and the full width is used.

First one is a bit trickier. To avoid javascript usage, we could add a second class to the wrapper. inline for small images and block for bigger images. Custom attributes sadly don't work because they are not accepted by maven-site-plugin. The tests for whether the image has a wrapper or not can also be updated matching this. The attribute display: block of the wrapper is the cause for these problems. It is needed for the horizontal scrolling of large images but causes a line-break, too, which only really matters in small inline images.

[jo2]

If someone cann add 'approved' label to this issue, I can do a PR.

[romani]

fix is merged.
Thanks a lot @jo2 for making our website nice ! it is become real pleasure to open web site on mobile.
I hope our users do not open checkstyle website in their leisure time (on mobile), and do this only at office (big screens). BUT maintainers do use mobile version a lot to recheck documentation and answer question of user.

[romani]

there was extra problem in FF(see details below) and it was addressed at #7357

how it was before:

according to @rnveach there should be some space between the text of the code snippet and its border. This already works in chrome (merged in #7302) and this pr fixes that for firefox.

[romani]

@jo2 , thanks a lot for additional fix. It is merged.