Looper

Added
- possibility to execute library module as a script: `python -m looper ...`

Changed
- in the summary page account for missing values when plotting; the value is disregarded in such a case and plot is still created
- show 50 rows in the summary table
- make links to the summary page relative
- long entries in the sample stats table are truncated with an option to see original value in a popover

Fixed
- inactive jQuery dependent components in the status page
- project objects layout in the summary index page
- inactivation of popovers after Bootstrap Table events
- non-homogeneous status flags appearance

Changed
- reduce verbosity of missing options; [Issue 174](https://github.com/pepkit/looper/issues/174)
- switch to [Bootstrap Table](https://bootstrap-table.com/) in the summary index page table and sample status tables

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)