This commit introduces initial Mode and ModTime support
for single filesystem files and webfiles.

The ipfs add options --preserve-mode and --preserve-mtime are
used to store the original mode and last modified time of the
file being added, the options --mode, --mtime and --mtime-nsecs
are used to store custom values.

A custom value of 0 is a no-op.

The preserve flags and custom options are mutually exclusive,
if both are provided the custom options take precedence.

This is needed for when ipfs get is used with the --output option to ensure the target for applying metadata is known.

…n time

…ixfs/ufs15

� Conflicts:
�	core/commands/files.go