replace "srt.replace()" in apply_filename_pattern() with equivalent re.sub()

the file_decoration passed into apply_filename_pattern() is formatted to lowercase to increase compatibility
the use of case sensitive srt.replace()

but because the newly implemented "time format" is case sensitive
the lowercasing the file_decoration will cause time format to be broken

in order to resolve this issue
I decided to replace every srt.replace() and in if "str" in x to regular expression (case insensitive) equivalent