Add GAIL algorithm

[isk03276]

Add GAIL algorithm with continuous action.

• Add relu activation function in helper_function
• Add accuracy-based early stopping to prevent discriminator from overfitting
• Add hybrid reward function (GAIL reward + task reward)

[tested in lunarlander continuous v2]

[lgtm-com]

This pull request introduces 2 alerts when merging 294837d into 3d106e5 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[lgtm-com]

This pull request introduces 2 alerts when merging 8eaeb2e into 3d106e5 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[lgtm-com]

This pull request introduces 2 alerts when merging 7913708 into 3f0f095 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[lgtm-com]

This pull request introduces 2 alerts when merging 7651f83 into a607f07 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[jiseongHAN]

we need to update readme.md

[lgtm-com]

This pull request introduces 2 alerts when merging beaa4ad into a607f07 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[lgtm-com]

This pull request introduces 2 alerts when merging 0832e7b into a607f07 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method

[lgtm-com]

This pull request introduces 2 alerts when merging eba07fd into a607f07 - view on LGTM.com

new alerts:

• 1 for Signature mismatch in overriding method
• 1 for `__init__` method calls overridden method