Swap "Merge Request" and "Branches" tabs in branch view in WebIDE
### Summary
When viewing a branch in Web IDE, especially one, connected to a merge request, we show dropdown above branch files in the left panel in the format:
```
branch-name | merge-request-id
```
Though when one clicks this dropdown to get a lit of all branches or all merge requests on this project, the order of the tabs in the dropdown is reversed:
```
merge-requests-list | branches-list
```
that is a bit confusing

### Possible fixes
I this we should swap panels in the dropdown to follow the `branch -> merge request` pattern
issue