[IMPROVEMENT] Use opaque cells for subscriptions table view

[Sameesunkaria]

@RocketChat/ios

Currently, the table view cells for SubscriptionsViewController have a transparent background when they are selected. This causes the cells to flicker when they are reloaded.

This will solve the flickering issue, without the need of UIView.performWithoutAnimation, which may also be responsible for a crash we recently started experiencing.

Possibly Closes #2036
This issue can be closed after beta testing, or a public release, if the crash no longer occurs.

[codecov]

Codecov Report

Merging #2053 into develop will decrease coverage by 0.27%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           develop    #2053      +/-   ##
===========================================
- Coverage    35.96%   35.68%   -0.28%     
===========================================
  Files          374      374              
  Lines        17437    17436       -1     
===========================================
- Hits          6271     6222      -49     
- Misses       11166    11214      +48

Impacted Files	Coverage Δ
...ubscriptionsList/SubscriptionsViewController.swift	39.23% <0%> (+0.37%)	⬆️
...iews/Cells/Subscription/BaseSubscriptionCell.swift	0% <0%> (ø)	⬆️
Rocket.Chat/API/Clients/PushClient.swift	0% <0%> (-33.34%)	⬇️
...Chat/Managers/Socket/Response/SocketHandlers.swift	38.63% <0%> (-25%)	⬇️
...Managers/Model/AuthManager/AuthManagerSocket.swift	12.82% <0%> (-14.75%)	⬇️
...et.Chat/Managers/Socket/Response/SocketError.swift	93.33% <0%> (-6.67%)	⬇️
...lers/Notification/NotificationViewController.swift	52.22% <0%> (ø)	⬆️

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[rafaelks]

Good finding!!! :-)