Firstly: 

It is obligatory to remove anything that may prevent water from reaching the skin, but one is forgiven for a very small amount such as dirt under the fingernails or in cracks in the feet, after trying hard to remove it. 

Al-Mardaaawi said in al-Insaaf (1/158): If there is a little dirt under the fingernails that prevents the water reaching under them, his purification is not valid. This was stated by Ibn ‘Aqeel. … And it was said that it is valid, and this is the correct view. 

This is the view to which the author (Ibn Qudaamah) was inclined, and it was the view favoured by Shaykh Taqiy ad-Deen [Ibn Taymiyah]. And it was said that it is valid on the part of one for whom it is difficult to avoid it, such as those who do handicrafts or hard work such as farming and so on. 

Shaykh Taqiy ad-Deen said: If there is something of such material anywhere on the body, such as blood, dough and the like, if it is a small amount, then it does not matter. End quote. 

If it is not possible to remove what has got stuck to the skin and there is a great deal of it, it is not pardoned. In that case you should wipe over it, as in the case of a plaster cast. Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If there is some barrier that is preventing the water from reaching the skin in that case you cannot say that that limb has been washed, but Shaykh al-Islam (may Allah have mercy on him) said: A small amount is forgiven, especially for one who has that problem. This applies to workers who use paint, because they often have one or two spots that they have either forgotten or could not find any means of removing them at present. According to the opinion of Shaykh al-Islam (may Allah have mercy on him), they are forgiven for this. But we learn from the hadeeth – which was narrated by Muslim (243) from ‘Umar ibn al-Khattaab (may Allah be pleased with him), which says that a man did wudoo’ and omitted a place the size of a fingernail on his foot. The Prophet (blessings and peace of Allah be upon) saw him and said: “Go back and do your wudoo’ properly,” so he went back, then he prayed – that something may not be forgiven even if it is small, if it is possible to remove it before the time for the prayer ends. In that case he should remove it, otherwise he should wipe over it and it becomes like a plaster cast.

End quote from Sharh al-Kaafi. 

Secondly: 

If the creator of a mobile app has not given permission to copy it, then it is not permissible to copy it. This has been explained in the answer to question no. 95173 

And Allah knows best.