Mentorship Requests and Request Detail Screen

[isabelcosta]

Description

Created Mentorship Requests List and the Request Detail screen.

• Mentorship Requests List has tabs for pending, past and all mentorship relations. One API is called to fetch the list of all mentorship requests, then before setting up the ViewPager fragments, the list are filtered. Each item of the list needs Mentor and mentee keywords, a function to help with this is partially implemented on PR Members List and Member profile #25
• Request Detail shows the notes, an initial text indicating if the request is sent by the user or received by.
• 2 buttons for reject and accepting a relation are shown if the relation is in the PENDING state and the end date hasn't passed yet.
• Delete button shows up if the relationship is in the PENDING state and was sent by me (the current user)
• A lot of logic for these ^^^ features is done on the RequestDetailActivity (hoping is not too complicated to understand, otherwise I'll add comments to it)
• Every button perfoms the proper action, accept, reject and delete a mentorship relation

Fixes #9
Fixes #8

Type of Change:

• Code

Code/Quality Assurance Only

• New feature (non-breaking change which adds functionality pre-approved by mentors)

How Has This Been Tested?

No tests were implemented yet :/
The UI was tested manually

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• Any dependent changes have been merged

Code/Quality Assurance Only

• My changes generate no new warnings

[isabelcosta]

Requests screen:

Empty requests tab:

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Detail of request sent by me (with scrollable text view to support small screens)

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Detail of request a user received (2 buttons to accept or reject)

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Detail of a request rejected by other users:

[isabelcosta]

@systers/maintainers-mentorship-android please review this.