Creating a new branch/merge request from issue page should be configurable

Summary

The changes implemented in gitlab-ce!10018 set the action to create a merge request as default in the dropdown box on the issue page. Depending on your workflow this really is not a good idea, especially when often rebasing branches the MR becomes very huge and unclear. We usually don't want to see every iteration of the code, so we only create a merge request when the code is ready for a first round of reviews. Having to set the dropdown to new branch every time is annoying.

Steps to reproduce

Create an issue. On the issue page the dropdown box selects "Create merge request" by default.

What is the current bug behavior?

Creating a new merge request is the default in the dropdown box on the issue page.

What is the expected correct behavior?

Creating a branch should be the default. Alternatively the default should be configurable per GitLab instance.

Possible fixes

Dirty hack to make "New branch" the default selection:

diff --git a/app/views/projects/issues/_new_branch.html.haml b/app/views/projects/issues/_new_branch.html.haml
index dba092c884..df7f5ee0d2 100644
--- a/app/views/projects/issues/_new_branch.html.haml
+++ b/app/views/projects/issues/_new_branch.html.haml
@@ -6,11 +6,11 @@
         %span.text
           Checking branch availability…
     .btn-group.available.hide
-      %input.btn.js-create-merge-request.btn-inverted.btn-success{ type: 'button', value: 'Create a merge request', data: { action: 'create-mr' } }
+      %input.btn.js-create-merge-request.btn-inverted.btn-success{ type: 'button', value: 'Create a branch', data: { action: 'create-branch' } }
       %button.btn.btn-inverted.dropdown-toggle.btn-inverted.btn-success.js-dropdown-toggle{ type: 'button', data: { 'dropdown-trigger' => '#create-merge-request-dropdown' } }
         = icon('caret-down')
       %ul#create-merge-request-dropdown.dropdown-menu.dropdown-menu-align-right{ data: { dropdown: true } }
-        %li.droplab-item-selected{ role: 'button', data: { value: 'create-mr', 'text' => 'Create a merge request' } }
+        %li{ role: 'button', data: { value: 'create-mr', 'text' => 'Create a merge request' } }
           .menu-item
             .icon-container
               = icon('check')
@@ -19,7 +19,7 @@
               %span
                 Creates a merge request named after this issue, with source branch created from '#{@project.default_branch}'.
         %li.divider.droplab-item-ignore
-        %li{ role: 'button', data: {  value: 'create-branch', 'text' => 'Create a branch' } }
+        %li.droplab-item-selected{ role: 'button', data: {  value: 'create-branch', 'text' => 'Create a branch' } }
           .menu-item
             .icon-container
               = icon('check')