Some improvements for Arabic (ar) localization

[Infocatcher]

Unfortunately seems I can't get feedback from original translator because his review already removed by AMO editors.

I'm use ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/latest/win32/xpi/ar.xpi and see that all accesskeys are translated, so we should do the same.
For example, File menu:

<menuitem
    id="menu_newNavigatorTab"
    label="لسان جديد"
    accesskey="ل"
    acceltext="Ctrl+T" />

(etc.)

And extension description should be translated too (install.rdf):

        <em:localized>
            <Description>
                <em:locale>ar</em:locale>
                <em:name>Private Tab</em:name>
                <em:description>Adds private tabs</em:description>
                <em:creator>Infocatcher</em:creator>
                <em:translator>infinity</em:translator>
            </Description>
        </em:localized>

[tahani5]

tahani5@7075ece

[Infocatcher]

tahani5/Private_Tab@7075ece

@tahani5, thanks! Updated: f69c4ac
(I leaved name unchanged)

Also please translate other new strings: /locale/ar/pt.properties

[tahani5]

Of course, with my pleasure

da67f4c

[Infocatcher]

Of course, with my pleasure

da67f4c

Thanks, updated: 529f29a

And two not yet translated lines:
/locale/ar/pt.properties#L27:

taskBarOpenNewPrivateTabDesc=Open a new tab in private browsing mode.

/locale/ar/pt.properties#L30:

taskBarOpenNewPrivateTabDescSM=Open a new private browsing tab.