[EPIC] Improvements in accessibility

[JuancaG05]

The app needs several improvements in accessibility terms. We'll group them here to have them all together. The related issues are:

• [a11y] 11.1.1.1a Non-text content (control elements) #4360
• [a11y] 11.1.1.1b Non-text content (graphics and objects) #4361
• [a11y] 11.1.3.1a Info and relationships (headings) #4362
• [a11y] 11.1.3.1d Info and relationships (form elements) #4363
• [a11y] 11.1.4.3 Contrast (minimum) #4364
• [a11y] 11.1.4.11 Non-text contrast #4365
• [a11y] 11.2.1.1 Keyboard #4366
• [a11y] 11.2.1.2 No keyboard trap #4367
• [a11y] 11.2.4.3 Focus order #4368
• [a11y] 11.2.4.7 Focus visible #4369
• [a11y] 11.2.5.1 Pointer gestures #4370
• [a11y] 11.2.5.3 Label in the name #4371
• [a11y] 11.3.1.1 Language of the software #4372
• [a11y] 11.4.1.2 Name-role value #4373
• [a11y] 11.7 User preferences #4374
• [a11y] Keyboard navigation in security passcode view #4447
• [a11y] Correct label for each activities and fragments #4458
• [a11y] Wrong name in toolbar Share View #4469