Looper

Added
- Ability to declare `required_executables` in a `PipelineInterface`, to trigger a naive "runnability" check for a sample submission
- A possibility to opt out of status page inclusion in the navbar

Changed
- The status tables now use DataTables jQuery plugin to make them interactive

Fixed
- Navbar links creation

Fixed
- Bug in `Sample` YAML naming, whereby a base `Sample` was being suffixed as a subtype would be, leading to a pipeline argument based on `yaml_file` that did not exist on disk.

Fixed
- Fixed various bugs related to populating derived attributes, including using attributes like `sample_name` as keys.
- Fixed a bug related to singularity attributes not being passed from a pipeline interface file.
- Fixed several bugs with incorrect version requirements.

Added
- Made `looper.Sample` include more specific functionality from `peppy`

Changed
- Status table creation is possible outside of `looper`.
- In the summary index page the plottable columns list is now scrollable
- Status page relies on the `profile.tsv` file rather than `*.log`; [Issue 159](https://github.com/pepkit/looper/issues/159)

Fixed
- In HTML reporting module, do not ignore objects which are neither HTMLs nor images in the summary, e.g. CSVs
- Restore parsing and application of pipeline-level computing resource specification from a pipeline interface file; [Issue 184](https://github.com/pepkit/looper/issues/184)
- Allow `ignore_flags` to properly modulate submission messaging; [Issue 179](https://github.com/pepkit/looper/issues/179)
- Do not display time-like summary columns as the plottable ones; [Issue 182](https://github.com/pepkit/looper/issues/182)

Added
- First implementation of pipeline interface 'outputs', so pipeline authors can specify items of interest produced by the pipeline.
- Functions and attributes on `Project` to support "outputs" (`interfaces`, `get_interfaces`, `get_outputs`)

Changed
- Start "compute" --> "compute_packages" transition
- `get_logger` moved to `peppy`

Fixed
- Prevent CLI option duplication in pipeline commands generated
- Make functional CLI spec of particular attribute on which to base selection of a subset of a project's samples ([`peppy` 298](https://github.com/pepkit/peppy/issues/298))

Changed
- Improved documentation
- Improved interaction with `peppy` and `divvy` dependencies