J1-nbinteract

**Python**

Features:

- The `j1-nbi` CLI now has a `--no-top-button` flag to remove the top-level
button.

Bug fixes:

- Python 3.4 doesn't support the `{**dict1, **dict2}` syntax, so we merge
dictionaries another way to support older versions of Python.
- Fixes an issue that broke `j1-nbi` CLI completely (52).
- The `j1-nbi` CLI spec argument didn't actually set the spec properly.

**JS**

Bug fixes:

- Fixes `j1-nbi-core` so that loading it in a webpage initializes the
j1-nbi variable properly.

**Python**

Changes:

- `nbi.publish()` and the `j1-nbi` CLI tool now require a Binder spec as
input.

Features:

- `nbi.publish()` and the `j1-nbi` CLI tool now allow for template
selection.
- The `j1-nbi` CLI tool gets a major overhaul with options to recurse into
subdirectories and output files in specified folders.

**JS**

Bug fixes:

- Fixed an issue where lots of error message were getting logged to the console
in the GitBook (https://github.com/SamLau95/j1-nbi/issues/41).

**Python**

Bugs fixed:

- Converting using `full.tpl` now correctly cells with ` HIDDEN`
(https://github.com/SamLau95/j1-nbi/pull/43/)
- Using `nbi.publish` now works on Python versions < 3.5
(https://github.com/SamLau95/j1-nbi/pull/43/)