Feature: Support for non standard layouts

Create option in settings to allow users to define which layout is used.

Example:
```json
{
  "svn.layout.trunk": "trunk",
  "svn.layout.branches": "branches",
  "svn.layout.tags": "tags"
}
```

Non Standard:
```json
{
  "svn.layout.trunk": "main",
  "svn.layout.branches": "versions",
  "svn.layout.tags": "stamps"
}
```
