Removed dependency on the gatsby image plugin

1. Removed dependency on image plugin
2. Image resolver API optimisation.
3. Format date string fix.

Added support for gatsby v4

1. Added support for gatsby v4.
2. Code refactoring.

3.1.1

Added support for new gatsby image plugin.
Requires the user to install gatsby-plugin-image, gatsby-plugin-sharp, gatsby-transformer-sharp to make it work.

Support for fetching data for only specified content-types and locales.

• Added support for fetching data for the specified content-types.
• Added support to exclude content-types while fetching data.
• Added support for fetching data for the specified locales.
• A combination of both content-types and locales also can be used to fetch data.
• Sync token caching issue fixed when expediteBuild is true.

Hotfix: Added Sync API params to fetch unpublished and deleted entries

• Added params entry_unpublished, entry_deleted, asset_unpublished and asset_deleted to sync updated data from contentstack.

Feat: added changes to support gatsby v4.

• Added custom error handler.
• Added backwards compatibility check for deprecating hook onPreInit.

Feat: added changes to support gatsby v3.

• Updated gatsby-source-filesystem to 3.
• Updated babel 6 to babel 7.
• Updated touchNode and deleteNode api.
• Added plugin options disableMandatoryFields, downloadImages in pluginOptionsSchema.

Fix: Added disableMandatoryFields config option and commitlint config.

• Added config option disableMandatoryFields: Disables mandatory fields check if a field is expected to be mandatory and value is null.
• Added commitlint config.
• Added semantic-release config.

BugFix: Reference field dependency tracking for inc builds

• getAllNodes replaced with getNodeById while resolving reference fields. Resolvers don't track resolved node dependencies in Gatsby v2 with getAllNodes, wherewith getNodeById track query dependencies to properly re-run queries for reference fields. Details are here in PR #91 description.

Hotfix: File fields inside group fields are not getting resolved

• File fields inside group fields are not getting resolved on 2.3.0 and above version