Clean up various use of escape/unescape functions for URL generation (#6334)

* Use PathUnescape instead of QueryUnescape when working with branch names

Currently branch names with a '+' fail in certain situations because
QueryUnescape replaces the + character with a blank space.

Using PathUnescape should be better since it is defined as:

// PathUnescape is identical to QueryUnescape except that it does not
// unescape '+' to ' ' (space).

Fixes #6333

* Change error to match new function name

* Add new util function PathEscapeSegments

This function simply runs PathEscape on each segment of a path without
touching the forward slash itself. We want to use this instead of
PathEscape/QueryEscape in most cases because a forward slash is a valid name for a
branch etc... and we don't want that escaped in a URL.

Putting this in new file url.go and also moving a couple similar
functions into that file as well.

* Use EscapePathSegments where appropriate

Replace various uses of EscapePath/EscapeQuery with new
EscapePathSegments. Also remove uncessary uses of various
escape/unescape functions when the text had already been escaped or was
not escaped.

* Reformat comment to make drone build happy

* Remove no longer used url library

* Requested code changes

routers/private/repository.go

@@ -6,7 +6,6 @@ package private
 
 import (
 	"net/http"
-	"net/url"
 
 	"code.gitea.io/gitea/models"
 
@@ -56,18 +55,18 @@ func GetRepository(ctx *macaron.Context) {
 func GetActivePullRequest(ctx *macaron.Context) {
 	baseRepoID := ctx.QueryInt64("baseRepoID")
 	headRepoID := ctx.QueryInt64("headRepoID")
-	baseBranch, err := url.QueryUnescape(ctx.QueryTrim("baseBranch"))
-	if err != nil {
+	baseBranch := ctx.QueryTrim("baseBranch")
+	if len(baseBranch) == 0 {
 		ctx.JSON(http.StatusInternalServerError, map[string]interface{}{
-			"err": err.Error(),
+			"err": "QueryTrim failed",
 		})
 		return
 	}
 
-	headBranch, err := url.QueryUnescape(ctx.QueryTrim("headBranch"))
-	if err != nil {
+	headBranch := ctx.QueryTrim("headBranch")
+	if len(headBranch) == 0 {
 		ctx.JSON(http.StatusInternalServerError, map[string]interface{}{
-			"err": err.Error(),
+			"err": "QueryTrim failed",
 		})
 		return
 	}