Fix #16951: Remove hardcoded 'Due date was' string

Signed-off-by: Damien Regad <dregad@mantisbt.org>
More i18n-friendly string for overdue label

Using a parameter within the language string avoids hardcoding of text
elements' order, which is better for translators.

Fixes #16951
Remove hardcoded file size unit 'k'

Fixes #16970

Signed-off-by: Damien Regad <dregad@mantisbt.org>
New API functions to print maximum file size

- get_filesize_info() returns the file size in the desired unit
- print_max_filesize() prints the span tag with maximum file size in
  desired unit, including tooltip in bytes

Updated language strings, refactored code to use the new functions

Issue #16970
Merge pull request #18 from dregad/hardcoded-strings

Hardcoded strings