Installer RTL Compat

- Compatibility for RTL with installer (includes rtl.css).
- Uses == true/false rather than empty() for conditions on
$txt['lang_rtl'] since it's a boolean, not an integer or null/not null.

Signed Off: Matthew P. Kerle / Labradoodle-360
<creativewebdsign@gmail.com>
Upgrade RTL Compat

- Added RTL Compatibility.
- Uses boolean operator rather than (!)empty() since the data type of
the variable is in fact a boolean.
- Gets rid of $upcontext['right_to_left'] which is undefined because
$txt is not in scope and is not populated at that point, which also
makes the install and upgrade scripts handle RTL in the same manner.

Signed Off: Matthew P. Kerle / Labradoodle-360
<creativewebdsign@gmail.com>
Fixed Tabbing of Script

- Fixed the indentation/tabbing of a script element in the head of
upgrade.php that was misaligned in editor and dom output.

Signed Off: Matthew P. Kerle  / Labradoodle-360
<creativewebdsign@gmail.com>
Fixed two typos

Just two small typo fixes to my last commits when I was looking them
over on GitHub.

Signed Off: Matthew P. Kerle / Labradoodle-360
<creativewebdsign@gmail.com>
Merge pull request #1685 from Labradoodle-360/install-upgrade-rtl-compat

Install and Upgrade RTL Compat