Add ability to use branches of other users

[SeanBryan51]

The user should be able to checkout branches of other users so that test suites can be reproduced by any user.

This change lets the user specify the path relative to the SVN root of the CABLE repository for each branch by specifying the path key in the configuration file. Remove the trunk and share_branch keys from the configuration file as this information is contained within path.

This change repurposes the name key for each branch to be an alias used internally by benchcab. This lets the user specify the directory name when checking out the branch, that is, name is the optional PATH argument to svn checkout`. This is useful in the case that we have a collision in branch names when checking out multiple branches.

Remove the -M PBS argument for sending emails in the job script as the default behaviour is sufficient.

Remove the user key as this is now redundant.

Update unit tests for check_config().

Fixes #61

[SeanBryan51]

TODO

• [x] If we are repurposing the name key in the configuration file to be an alias. This should be an optional key. By default we should use the base name of the path key.

[ccarouge]

Do we want to make name optional? And use the stem of path if not provided?