scan-tree: Unify gitweb.* and cgit.* settings into one config option.

After some back and forth with Jamie and René, it looks like the git
config semantics are going to be like this:

- gitweb.category maps to the cgit repo config key "section"
- gitweb.description maps to the cgit repo config key "desc"
- gitweb.owner maps to the cgit repo config key "owner"
- cgit.* maps to all cgit repo config keys

This option can be enabled with "enable-git-config=1", and replaces
all previous "enable-gitweb-*" config keys.

The order of operations is as follows:

- git config settings are applied in the order that they exist in
  the git config file
- if the owner is not set from git config, get the owner using the
  usual getpwuid call
- if the description is not set from git config, look inside the
  static $path/description file
- if section-from-path=1, override whatever previous settings were
  inside of git config using the section-from-path logic
- parse $path/cgitrc for local repo.* settings, that override all
  previous settings

cgit.h

@@ -200,9 +200,6 @@ struct cgit_config {
 	int case_sensitive_sort;
 	int embedded;
 	int enable_filter_overrides;
-	int enable_gitweb_owner;
-	int enable_gitweb_desc;
-	int enable_gitweb_section;
 	int enable_http_clone;
 	int enable_index_links;
 	int enable_commit_graph;
@@ -211,6 +208,7 @@ struct cgit_config {
 	int enable_remote_branches;
 	int enable_subject_links;
 	int enable_tree_linenumbers;
+	int enable_git_config;
 	int local_time;
 	int max_atom_items;
 	int max_repo_count;
@@ -285,6 +283,7 @@ extern struct cgit_repolist cgit_repolist;
 extern struct cgit_context ctx;
 extern const struct cgit_snapshot_format cgit_snapshot_formats[];
 
+extern char *cgit_default_repo_desc;
 extern struct cgit_repo *cgit_add_repo(const char *url);
 extern struct cgit_repo *cgit_get_repoinfo(const char *url);
 extern void cgit_repo_config_cb(const char *name, const char *value);