systemctl: ellipsize job list only when necessary, highlight running

I was debugging systemd waiting on a missing disk, and noticed
that the job listing could use some polishing. Jobs that are
actually running are highlighted, so it's easier to see what
very actually waiting for.

Also, the needed widths are precalculated, to use available columns
more ecomically.

src/shared/util.h

@@ -647,4 +647,11 @@ static inline bool logind_running(void) {
         return access("/run/systemd/seats/", F_OK) >= 0;
 }
 
+static inline unsigned decimal_str_max(unsigned x) {
+        unsigned ans = 1;
+        while (x /= 10)
+                ans ++;
+        return ans;
+}
+
 int unlink_noerrno(const char *path);