`host` parsed from user login (if present) for Emails

Description:

Related issue (if applicable): n/a

This was a report made on Discord where the URL should have worked (imo):

mailtos://?smtp=mobile.charter.net&pass=password&user=name@spectrum.net

Apprise wasn't smart enough to pull the spectrum.net hostname from the user login for the host until this PR. The user above can still use the URL:

mailtos://spectrum.net?smtp=mobile.charter.net&pass=password&user=name@spectrum.net

After this PR, the first URL will work. To avoid ambiguity, emails can now also be specified in the hostname if content was parsed elsewhere; hence the following URL is also valid now:

mailtos://Jason Smith<jsmith%40yahoo.ca>?smtp=mobile.charter.net&pass=password&user=name@spectrum.net
- Note: %40 == @. The idea is if you don't specify a hostname, you're not restricted from putting in your emails you want to transmit to. This becomes the to and flows with current design.

Checklist

[x] The code change is tested and works locally.
[x] There is no commented out code in this PR.
[x] No lint errors (use flake8)
[x] 100% test coverage

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in as follows:
python3 -m venv apprise

# Change into our new directory
cd apprise

# Activate our virtual environment
source bin/activate

# Install the branch
pip install git+https://github.com/caronc/apprise.git@email-host-detection-from-source

# Test out the changes with the following command:
apprise -t "Test Title" -b "Test Message" \
  "mailtos://?smtp=mobile.charter.net&pass=password&user=name@spectrum.net"

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.27%. Comparing base (6cd528c) to head (ffb2dfd).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1095 +/- ## ======================================= Coverage 99.27% 99.27% ======================================= Files 138 138 Lines 17954 17964 +10 Branches 3663 3667 +4 ======================================= + Hits 17824 17834 +10 Misses 121 121 Partials 9 9 ```

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caronc / apprise