MPDX-7727 Add organization to add donation modal

[caleballdrin]

Description

https://jira.cru.org/browse/MPDX-7727
In the helpscout ticket mentioned in the title, the user has multiple orgs that he receives donations with and he says that the add donation modal in angular has a way to choose a specific org, while in react, it doesn't.  I don't see this org selection option on the add donation modal in my angular version of MPDX to provide a screenshot, but I'm also not associated with multiple orgs.

The user also requested the ability to choose a date by just picking a date rather than needing to hit "Ok" when not on mobile.

Changes I made

• The autocomplete was only showing the designation accounts from the first organization. Show all designation accounts in all organizations by flattening designationAccounts
• Changing MobileDatePicker to DatePicker so it will automatically show different date pickers on Web vs Mobile.

Checklist:

• I have given my PR a title with the format "MPDX-(JIRA#) (summary sentence max 80 chars)"
• I have applied the appropriate labels. (Add the label "On Staging" to get the branch automatically merged into staging.)
• I have requested a review from another person on the project

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[dr-bizz]

This looks great! Please can you ask Scott to QA this before we put t live.