Fix invalid HTML

- Remove </input>
- Move <input> tag within table cell
- missing <td> tag (align with master)
Modify generated config_inc.php file

- Remove leading tab character
- Remove trailing '?>' tag
Simplify config file generation

- Use a ternary operator
- Remove redundant instructions to manually create the config file in
  label: what the admin needs to do should be clear enough with the
  error message and the text below.
- Improve message to add lines to config file
Remove table background color

This makes the display of the various sections consistent (prior to
this, some had borders around cells and others didn't).

Also, bgcolor attribute is not supported in HTML5 so it makes sense to
remove it for future compatibility.
Remove ellipsis
Add 'Installation complete' section

This makes the look of the installer's last printed lines consistent
with the rest of the page.
Start with 0 if given invalid install step
Display section title when starting with step 2