Add Subtitle generator feature

[Gauravjeetsingh]

Current feature implementation:

• Generate subtitles by click of a button
• Download the subtitle anytime, even after app is closed and launched again
• Ability to delete subtitle file from the app itself
• Subtitles are generated in the srt format

Future scope

• Support orther subtitle format like vtt
• Ability to set a start time in subtitle

@saintsoldierx Can you please review the UI and let me know if it needs any change?

Sidenote: It doesn't open the downloaded srt file automatically, I used notepad to open it manually from downloads. Contents of file are not clearly visible, this is what it saved:

1
00:00:00:00 --> 00:00:04:827
ਦੀਦਨੇ ਦੀਦਾਰ ਸਾਹਿਬ ਕਛੁ ਨਹੀ ਇਸ ਕਾ ਮੋਲੁ ॥

2
00:00:04:827 --> 00:00:06:1507
ਪਾਕ ਪਰਵਦਗਾਰ ਤੂ ਖੁਦਿ ਖਸਮੁ ਵਡਾ ਅਤੋਲੁ ॥੧॥

3
00:00:06:1507 --> 00:00:08:1546
ਦਸ੍ਤਗੀਰੀ ਦੇਹਿ ਦਿਲਾਵਰ ਤੂਹੀ ਤੂਹੀ ਏਕ ॥

4
00:00:08:1546 --> 00:00:09:2506
ਕਰਤਾਰ ਕੁਦਰਤਿ ਕਰਣ ਖਾਲਕ ਨਾਨਕ ਤੇਰੀ ਟੇਕ ॥੨॥੫॥