Make main col width dynamic

[crftwrk]

Main content col must have a fixed width <div class="col-md-8 col-lg-9">. Dynamic col class isn't enough, because if content has e.g. a larger image col uses the entire screen width and sidebar is pushed to bottom.

This PR replaces the fixed col width classes with function <div class="<?php echo bootscore_main_col_class(); ?>">, which returns to <div class="col-md-8 col-lg-9"> if sidebar is active and to <div class="col"> if no sidebar is active. In conclusion, if no sidebar is active, content uses entire width. No empty whitespace anymore.

Adds a sidebar to *-full-width-image.php templates.

@justinkruit if you like it, merge it.

[justinkruit]

Just for cleanness, do we want to use <?php echo [] ?> or <?= [] ?>? My personal preference is always <?= because it looks cleaner to me and is still a clear indication something is echoing.

[crftwrk]

Your ideas are always better than mine. Want to change that quickly?

[justinkruit]

Sure! I'll do it tomorrow though, going out for the evening 😉

[justinkruit]

Will do it in a seperate PR, as there are more places this can be done.