* Merge defaults and config deeply in set_defaults
The Object.assign method performs a shallow merge, thus it can lose
properties in nested objects. For example, if config.bar = { foo: bar }
then it would entirely replace defaults.bar and self.config.bar.height
would be undefined. The deepmerge library is a lightweight module that
merges enumerable attributes deeply. In the above example,
self.config.bar would then be {foo: bar, height: 20}.
I think this commit also retroactively applies some previous changes to
dist/frappe-gantt.js and dist/frappe-gantt.js.map from commits: 241c65db697475a3a17324f4c613d28353f89a8c,
1926ddbd48f1ff0bd7a0d49cadf14fcd415c3bfd, and be45a9656ffd482e1611198158b6032c965e1309.
* Define bar corner radius on initialization
Allows this property to be set without changing source code. Requires
deep merge of default and config objects added in commit f32e76af7733515f10a9adc004100e57f794f804
* Fix bug causing TypeError when config parameter is undefined
Fixes issue when optional config parameter is unspecified since
Deepmerge throws error "Cannot convert undefined or null to object"
in such cases.
* * adjusted the library to support both string css selectors and a raw svg element when resetting its internal variables
* * changes parent_element to use const again instead of let
* * updated the element selection logic to include checking for an html element and finding a child svg object
* * updated parameter comment and exception message to mention both html and svg dom element support
* Code formatting
