Contribution notifications not always showing

[NejcZdovc]

Success notification is not working correctly.

2. Add more detailed error notifications

• auto contribute table is empty
• not enough funds

[LaurenWags]

@NejcZdovc Test Plan in PR (brave/brave-core#896) covers:

• Notification for successful tip (logged no notification after successful tip - follow up to 2114 #2275 for this)
• Notification for unsuccessful auto-contribution (when there is not enough funds)

Per description of issue, with this issue should we also be testing the following?

• Notification for successful auto-contribution
• Notification for unsuccessful auto-contribution (when the auto-contribute table is empty)

cc @kjozwiak

[LaurenWags]

Verified passed with

Brave	0.57.8 Chromium: 71.0.3578.53 (Official Build) beta(64-bit)
Revision	599fb72e740eab9d10609f1ed28a2ad669f82c1a-refs/branch-heads/3578@{#669}
OS	Mac OS X

• Verified notification for unsuccessful contribution (when there are not enough funds). Note, while a notification occurs, this notification does not match image in PR. Confirmed in slack that this is expected.
  

• Verified notification for successful contribution
  

Logged these follow-up issues:

• No notification for successful tip: no notification after successful tip - follow up to 2114 #2275
• Per comment above (link), I’m unsure if this PR should cover a notification for unsuccessful contribution (when auto-contribute table is empty) since it was mentioned in original issue description. Anyhow, since no notification is generated, logged no notification when a-c table is empty and contribution is attempted - follow up to 2114 #2294

Verified passed with

Brave	0.57.8 Chromium: 71.0.3578.53 (Official Build) beta(64-bit)
Revision	599fb72e740eab9d10609f1ed28a2ad669f82c1a-refs/branch-heads/3578@{#669}
OS	Windows 7

• Verified notification for unsuccessful contribution
• Verified notification for successful contribution

Issues:
#2275
#2294

Verified PASSED with Ubuntu 17.10

Brave	0.57.8 Chromium: 71.0.3578.53 (Official Build) beta(64-bit)
Revision	599fb72e740eab9d10609f1ed28a2ad669f82c1a-refs/branch-heads/3578@{#669}
OS	Linux

• Verified notification for unsuccessful contribution
• Verified notification for successful contribution

Issues:
#2275
#2294