mpdf: Upgrade to 5.7.3
i18n: Package fonts with the Thai language pack

This patch also makes a slight edit to mPDF to allow better detection of
substitions in characters, as the DejaVu fonts shipped do not support Thai
glyphs.
i18n: Proper rtl layout for staff navigation
i18n: rtl: Fix button floating layout for RTL
i18n: rtl: Fix tab display for rtl viewers
i18n: Fix help tip popup for RTL display
i18n: rtl: Fix ticket thread layout
i18n: rtl: Fix dropdowns on action buttons
i18n: rtl: Fixup redactor rtl blocks
i18n: rtl: Fixup filedrop for rtl display
i18n: rtl: Fix quick note layout for rtl display
i18n: pdf: Use Adobe CJK output be default
i18n: rtl: Use linebreaks mode with Redactor and support rtl
Merge pull request #1356 from greezybacon/issue/intl-ui-print

i18n: Fix several issues with right-to-left layout

Reviewed-By: Peter Rotich <peter@osticket.com>