pl-PL: bring up to date and improve (#2964)

Applying for issue(s):

String 6514 #2414
String 96 and 606 #2430
String 6515 - 6519 #2446
String 5836 #2466
Strings 6520-6526 #2472
String 6527 #2473
String 6322 #2492
String 6528-6529 #2501
Strings 6530-6532 + Scenario descriptions #2509
String 5836, 6515, 6516, 6517 #2511
String 6533-6535 #2520
String 6491, 6493, 6536 #2527
String 6537, 6538 #2535
Strings 6540-6541 #2550
String 6539 #2551
Strings 6137-6138 + 6542-6543 #2562
String 6544 #2563
String 6545, 6546 #2572
String 6547 #2578
String 6548 #2594
Strings 6549-6550 #2602
Strings 6551-6576 #2609
String 6577-6579 #2620
String 6580-6581 #2625
String 6582 #2631
String 6583-6585 #2641
String 6586-6588 #2650
String 6589-6590 #2658
String 6591-6592 #2659
String STR_6593 #2678
String STR_6594 #2679
Strings 6595-6596 #2692
Strings 6597-6612 #2720
STR_6613 #2732
Strings 6614-6617 #2755
String 6618-6622 #2769
WWTT Flying saucers vehicles name change. #2781
String 6623-6626 #2794
Strings 0097-0607 #2801
String 6627 #2806
String 6628 #2814
Strings 6629–6630 #2815
Strings 6631–6637 #2821
Strings 6638-6639 #2826
String 6640 #2836
Strings 6641–6643 #2843
String 6644-6645 #2854
String 6646–6647 #2868
String 6648 #2869
Strings 6649–6651 #2875
STR_6652 #2881
String 6653–6655 #2884
String 6656 #2894
String 6657–6658 #2895
Strings 6659–6660 #2897
Strings 6661–6662 #2909
Strings 6663–6670 #2917
Strings 6671–6672 #2928
String 6673 #2936
String 6674 #2938
Strings 6675-6676 #2941
Strings 6677–6709 #2945
String 0098, 0608, 6541 #2960