200 as a user i want to provide my own subscriptions to the resource alert system

[sgobotta]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

This PR provides:

• Support for adding snackbar hooks during Resource operations
• Documentation update for the Resource component

Closes #200

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

The following options in bold are required for a PR approval. Please check the boxes only if necessary, it help us minimizing the reviewing process.

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (develop@aabf8ff). Click here to learn what that means.
The diff coverage is 19.04%.

@@            Coverage Diff             @@
##             develop     #206   +/-   ##
==========================================
  Coverage           ?   40.15%           
==========================================
  Files              ?       96           
  Lines              ?      787           
  Branches           ?       30           
==========================================
  Hits               ?      316           
  Misses             ?      468           
  Partials           ?        3

Impacted Files	Coverage Δ
src/constants/ui.content.default.js	50% <ø> (ø)
src/store/modules/crud.js	62.5% <ø> (ø)
src/plugins/vuex/subscriptions.js	100% <ø> (ø)
src/components/Resource/src/Resource.vue	95.23% <ø> (ø)
src/components/Admin/src/Alerts.vue	100% <ø> (ø)
src/templates/src/index.js	100% <ø> (ø)
src/main.js	0% <0%> (ø)
src/components/Resource/src/defaults.js	44.44% <20%> (ø)

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