gitweb: Create Gitweb::Util module

gitweb: Create Gitweb::Util module

Create Gitweb::Util module in 'gitweb/lib/Gitweb/Util.pm'
to store the git utility subroutines related to gitweb.

This module include subroutines in various categories
such as git utility subs invoking git commands, git
utility subs accessing git repository, mimetype related
subs and HTML output utility subs.

Subroutines moved:
	git_get_head_hash
	git_get_full_hash
	git_get_short_hash
	git_get_hash
	git_get_type
	git_get_hash_by_path
	git_get_path_by_hash
	git_get_last_activity
	git_get_references
	git_get_rev_name_tags
	git_get_heads_list
	git_get_tags_list
	mimetype_guess_file
	mimetype_guess
	blob_mimetype
	blob_contenttype
	guess_file_syntax
	run_highlighter
	fill_from_file_info
	is_deleted
	is_patch_split

Update 'gitweb/Makefile' to install Gitweb::Util alongside gitweb.

Signed-off-by: Pavan Kumar Sunkara <pavan.sss1991@gmail.com>