Update muscle and exercise lists

[hariclerry]

What does this PR do?

There are already lists of muscles and exercises in the system, so this PR updates or adds more data to the existing data.

Description of Task to be completed?

Update list of available muscles as well as the exercises.

How should this be manually tested?

1. Follow the setup instructions in README.rst
2. Run the python manage.py runserver command to start the app.
3. Log in as an admin with default username: admin and default password: admin.
4. From the dashboard, click on the Exercises tab, from the drop down menu click on the muscle overview link.
5. From the overview page you should be able to see list of muscles with the new added muscles, hover over the muscles to see the list of exercises added to them.

Screen Shots

Page showing Muscle1 overview and list of exercises

Page showing Muscle2 overview and list of exercises

Any background context you want to provide?

New muscles added are:

1. Lateral deltoid
2. Posterior Deltoid
3. Forearms
4. Erector spinae. This muscle already existed in the muscle lists but didn't have an SVG image and exercises. So I added an SVG image and lists of exercises to it.

What are the relevant pivotal tracker stories?

#157731621

[hariclerry]

Hey guys, can you please review my PR and let me know what you think.

[coveralls]

Pull Request Test Coverage Report for Build 343

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.079%

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Totals
Change from base Build 319:	0.0%
Covered Lines:	12426
Relevant Lines:	13350

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💛 - Coveralls

[dondrzzy]

@hariclerry , good stuff. Make sure you incoporate the hover over those muscles on the image and display the exercises. Add the paths to the svg in muscles.js. Back muscles to musclesBack and front muscles to musclesFront oterwise, its okay.

[hariclerry]

@dondrzzy, I have incorporated the hover over for muscles. The exercises were already added. Thanks for your help with muscle hovering over effects.